DENTAL  DEPARTMENT 


A  TEXT-BOOK 


OF 


HISTOLOGY 

INCLUDING  MICROSCOPIC  TECHNIC 

BY 

A.   A*  JBOHM,  1VL  D.,  and  M.  VON   DAVIDOFF,  M.  D. 

of  the  Anatomical  Institute  in  Munich 

Edited,  with  Extensive  Additions  to  both  Text  and   Illustrations 


G.  CARL  HUBER,  M*D. 

Junior  Professor  of  Anatomy  and  Director  of  the  Histological  Laboratory 
University  of  Michigan 


Authorized  Translation  from  the  Second  Revised  German  Edition 

BY 

HERBERT  H.   GUSHING,  M.D. 
Demonstrator  of  Histology  and  Embryology,  Jefferson  Medical  College,  Philadelphia 


WITH  351  ILLUSTRATIONS 


PHILADELPHIA  AND  LONDON 

B.  SAUNDERS  &  COMPANY 

J90J 


R 


COPYRIGHT,  1900, 
BY  W.  B.  SAUNDERS  &  COMPANY 


f 


PRESS   OF 
3.    SAUNDERS    &    COMPANY 


TO  THEIR  TEACHER 
PROFESSOR   C  VON  KUPFFER 

THIS  BOOK  IS  DEDICATED  BY 

THE  GRATEFUL  AUTHORS 


EDITOR'S  PREFACE. 


THE  "  Text-book  of  Histology  "  by  Bohm  and  v.  Davidoff,  as  stated 
by  the  authors  in  the  preface  to  the  first  edition,  presents  as  fully  as 
possible,  from  both  the  theoretic  and  technical  standpoints,  the  subject- 
matter  of  the  lectures  and  courses  in  histology  given  to  students  in  the 
University  of  Munich.  The  authors  further  state  that  in  the  completion 
of  their  work  they  had  the  constant  aid  and  advice  of  Professor  von 
Kupffer,  and  had  at  their  disposal  the  sections  in  the  collection  of  the 
histologic  laboratory  in  Munich,  which  were  freely  used  in  the  selection 
and  preparation  of  the  illustrations  accompanying  the  text. 

The  excellence  of  the  text  and  illustrations  of  the  German  edition, 
attested  by  all  familiar  with  the  work,  and  the  cordial  reception  which  it 
has  received  from  both  students  and  investigators,  justify  the  belief  that 
an  English  translation  will  meet  with  approval  from  American  and 
English  teachers  and  students. 

In  the  preparation  of  this  American  edition  the  editor  has  retained 
substantially  all  the  subject-matter  and  illustrations  of  the  second  German 
edition,  although  certain  minor  changes  in  the  arrangement  of  the  text 
seemed  desirable.  Additions  to  the  German  text  have  been  freely  made. 
The  sections  on  the  Motor  and  Sensory  Nerve -endings  and  on  the  Spinal 
and  Sympathetic  Ganglia  have  been  greatly  expanded,  and  the  Innerva- 
tion  of  Glands  and  Organs  has  been  considered  much  more  fully  tjaan  in 
the  original.  Our  knowledge  of  the  normal  function  of  tissues  and 
organs  is  so  dependent  on  a  correct  understanding  of  their  innervation 
that  this  subject  seemed  deserving  of  fuller  consideration  than  is  generally 
given  it  in  text-books  of  this  scope.  The  glands  with  internal  secretion 
have  also  been  considered  more  fully  than  in  the  original  text,  their  im- 
portance necessitating  such  treatment.  More  than  one  hundred  illustra- 
tions, the  majority  of  them  from  original  drawings,  have  also  been  added. 
In  making  these  and  other  minor  additions  the  editor  has  striven  to 
stamp  his  own  work  with  the  excellent  features  of  the  German  text,  and 
trusts  that  his  endeavors  may  have  added  to  the  usefulness  of  the  book. 

The  editor  acknowledges  with  pleasure  his  indebtedness  to  Dr. 
Herbert  H.  Gushing  for  his  excellent  and  accurate  translation,  and  for 
suggestions  received  from  him.  The  publishers,  Messrs.  Saunders  & 
Company,  have  shown  throughout  the  greatest  interest  in  the  work,  and 
deserve  the  gratitude  of  the  editor  for  their  ready  acquiescence  in  all 
suggestions  made  by  him,  for  the  excellent  reproduction  of  his  drawings, 
and  for  the  suggestions  made  to  him.  The  editor  is  particularly  in- 
debted to  his  able  assistant,  Dr.  Lydia  M.  De  Witt,  for  valuable  assistance 
rendered,  more  especially  in  the  tedious  work  of  proof-correction,  for 
which  he  expresses  his  sincere  appreciation  and  gratitude. 

G.  CARL  HUBER. 

UNIVERSITY  OF  MICHIGAN,  ANN  ARBOR,  MICH. 
October,  igoo. 


CONTENTS. 


INTRODUCTION  TO  MICROSCOPIC  TECHNIC 

PAGE 

Microscope  and  Its  Accessories 17 

Microscopic  Preparations      20 

Fixing  Methods 22 

Infiltration  and  Imbedding 25 

Paraffin 26 

Celloidin     .    .        28 

Celloidin-paraffin 30 

Microtomes  and  Sectioning 30 

Further  Treatment  of  the  Section 38 

Fixation  to  the  Slide  and  Removal  of  Paraffin 38 

Staining      40 

Section  Staining , 40 

Staining  in  Bulk 45 

Preparation  of  Permanent  Specimens 46 

Introduction  to  Methods  of  Injection      48 


GENERAL  HISTOLOGY. 
L  THE  CELL* 

Cell-body 52 

Nucleus 55 

Nuclear  and  Cell-division 56 

Mitosis  or  Karyokinesis  (Indirect  Cell-division) 57 

Prophases 60 

Metaphases 62 

Anaphases 63 

Telophases 64 

Heterotypic  Form  of  Mitosis 64 

Amitosis      .    .  64 

Process  of  Fertilization 65 

Chromatolysis     ....        68 

Technic  for  the  Cell 68 

IL  TISSUES. 

Epithelial  Tissues 74 

Simple  Epithelium 76 

Simple  Squamous  Epithelium 76 

Simple  Cubic  Epithelium 76 

Simple  Columnar  Epithelium 76 

Pseudostratified  Columnar  Epithelium 77 

Stratified  Epithelium 77 

Stratified  Squamous  Epithelium 78 

Transitional  Epithelium 79 

Stratified  Columnar  Epithelium 79 

.   Glandular  Epithelium 81 

Gland-cell 8l 

General  Consideration  of  the  Structure  and  Classification  of  Glands  ...  82 

7 


8  CONTENTS. 

Epithelial  Tissues — Glandular  Epithelium  (Continued).  PAGE 

Remarks  on  the  Process  of  Secretion 85 

Neuro-epithelium  85 

Mesothelium  and  Endothelium 85 

Technic  for  Epithelial  Tissues 87 

Connective  Tissues 89 

Mucous  Connective  Tissue 92 

Reticular  Connective  Tissue 92 

Fibrous  Connective  Tissue 93 

Adipose  Tissue 99 

Cartilage 99 

Bone 103 

Structure  of  Bone 103 

Development  of  Bone 107 

Technic  for  Connective  Tissues 117 

Muscular  Tissues 1 23 

Nonstriated  Muscle-cells 124 

Striped  Muscle-fibers  .  124 

Cardiac  Muscle-cells 132 

Technic  for  Muscular  Tissue 132 

Nervous  Tissues 133 

Nerve-cells  or  Ganglion  Cells  ;  Cell-bodies  of  Neurones 134 

Nerve-fibers 142 

Peripheral  Nerve  Terminations 147 

Technic  for  Nervous  Tissues  .  , 164 


SPECIAL   HISTOLOGY. 

L  BLOOD  AND   BLOOD-FORMING   ORGANS,  HEART, 
BLOOD-VESSELS,  AND  LYMPH-VESSELS. 

Blood  and  Lymph 168 

Formation  of  Blood 168 

Red  Blood-corpuscles        169 

White  Blood-corpuscles 173 

Blood  Platelets  and  Blood  Plasma 176 

Behavior  of  Blood-cells  in  the  Blood  Current 177 

Lymphoid  Tissue,  Lymph-nodules,  and  Lymph-glands 177 

Spleen  180 

Bone-marrow      185 

Thymus  Gland 188 

IL  CIRCULATORY  SYSTEM. 

Vascular  System 190 

Heart 190 

Blood-vessels      193 

Arteries 194 

Veins , 197 

Capillaries 198 

Anastomoses,  Retia  Mirabilia,  and  Sinuses 199 

Lymphatic  System 200 

Lymph-vessels 200 

Lymph-capillaries,  Lymph-spaces,  and  Serous  Cavities 201 

Carotid  Gland  (Glandula  Carotica,  Glomus  Caroticum) 202 

Technic  for  Blood  and  Blood-forming  Organs 203 

Technic  for  Circulatory  System 210 

IIL  DIGESTIVE  ORGANS. 

Oral  Cavity 211 

Teeth , 213 

Structure  of  the  Adult  Tooth 213 


CONTENTS.  9 

Oral  Cavity — Teeth  {Continued}.  PAGE 

Development  of  the  Teeth 217 

Tongue 221 

Lingual  Mucous  Membrane  and  Its  Papillae 22 1 

Taste-buds 223 

Lymph-follicles  of  the  Tongue  (Folliculi  Linguales)  and  the  Tonsils     .    .  225 

Glands  of  the  Oral  Cavity         227 

Salivary  Glands      . 228 

Parotid  Gland  (Serous  Gland) 228 

Sublingual  Gland  (Mucous  Gland) 228 

Submaxillary  Gland  (Mixed  Gland) 230 

Small  Glands  of  the  Mouth 231 

Pharynx  and  Esophagus       233 

Stomach  and  Intestines     .    .        .         235 

General  Structure  of  the  Intestinal  Mucous  Membrane 235 

Stomach 237 

Small  Intestine 243 

Large  Intestine,  Rectum,  and  Anus 249 

Blood,  Lymph,  and  Nerve  Supply  of  the  Intestine 251 

Secretion  of  the  Intestine  and  the  Absorption  of  Fat 256 

Liver 257 

Pancreas 265 

Technic  for  Digestive  Organs 269 

IV.  ORGANS  OF  RESPIRATION. 

Larynx 275 

Trachea 276 

Bronchi,  their  Branches,  and  the  Bronchioles 277 

Respiratory  Bronchioles,  Alveolar  Ducts,  and  Infundibula 279 

Thyroid  Gland 284 

Parathyroid  Glands 285 

Technic  for  Organs  of  Respiration 286 

V*  GENITO-URINARY  ORGANS. 

Urinary  Organs 287 

Kidney 287 

Pelvis  of  the  Kidney,  Ureter,  and  Bladder 300 

Suprarenal  Glands 3O1 

Technic  for  Urinary  Organs  and  Suprarenal  Body 305 

Female  Genital  Organs  .  , 3°6 

Ovum  3°6 

Ovary 306 

Fallopian  Tubes,  Uterus,  and  Vagina 316 

Male  Genital  Organs 323 

Spermatozoon 323 

Testes 324 

Excretory  Ducts 329 

Spermatogenesis 334 

Technic  for  Reproductive  Organs 34° 

VI*  THE  SKIN  AND  ITS  APPENDAGES. 

Skin  (Cuds) 341 

Hair 350 

Nails 355 

Glands  of  the  Skin 357 

Sweat-glands      357 

Sebaceous  Glands      35$ 

Mammary  Glands 359 

Technic  for  the  Skin  and  Its  Appendages 3^2 

VIL  THE  CENTRAL  NERVOUS  SYSTEM. 

Spinal  Cord 365 

Cerebellar  Cortex 372 


10  CONTENTS. 

PAGE 

Cerebral  Cortex 375 

Olfactory  Bulb 379 

Epiphysis  and  Hypophysis 3^° 

Ganglia 382 

General  Survey  of  the  Relations  of  the  Neurones  to  One  Another  in  the  Central 

Nervous  bystem 389 

Neuroglia 392 

Membranes  of  the  Central  Nervous  System 393 

Blood-vessels  of  the  Central  Nervous  System 397 

Technic  for  Central  Nervous  System  .  • 397 

VIIL  EYE. 

General  Structure 407 

Development  of  the  Eye 407 

Tunica  Fibrosa  Oculi 409 

Sclera 409 

Cornea         410 

Vascular  Tunic  of  the  Eye 412 

Choroid,  Ciliary  Body,  and  Iris « 412 

Internal  or  Nervous  Tunic  of  the  Eye 418 

Pigment  Layer 418 

Retina , 418 

Region  of  the  Optic  Papilla 420 

Region  of  the  Macula  Lutea 421 

Ora  Serrata,  Pars  Ciliaris  Retinae,  and  Pars  Iridica  Retinas 422 

Miiller's  Fibers  of  the  Retina 422 

Relations  of  the  Elements  of  the  Retina  to  One  Another 423 

Optic  Nerve  425 

Blood-vessels  of  the  Optic  Nerve  and  Retina 426 

Vitreous  Body 427 

Crystalline  Lens 428 

Fetal  Blood-vessels  of  the  Eye , 429 

Interchange  of  Fluids  in  the  Eyeball 429 

Protective  Organs  of  the  Eye 430 

Lids  and  Conjunctiva 430 

Lacrimal  Apparatus 432 

Technic  for  the  Eye 433 

IX.  ORGAN  OF  HEARING* 

External  Ear 435 

Middle  Ear         437 

Internal  Ear 439 

Utriculus  and  Sacculus 441 

Semicircular  Canals 442 

Cochlea 443 

Organ  of  Corti 447 

Nerves  and  Blood-vessels  of  the  Cochlea 452 

Development  of  the  Labyrinth 454 

Technic  for  Organ  of  Hearing 455 

X.  ORGAN  OF  SMELL. 

Technic  for  Nasal  Mucous  Membrane 457 

XL  GENERAL  CONSIDERATIONS  OF  THE  SPECIAL 
SENSE-ORGANS. 


REFERENCES  TO  LITERATURE 461 

INDEX , 483 


ILLUSTRATIONS. 


FIG.  PAGE 

1.  Microscope 18 

2.  Box  for  imbedding  tissues 26 

3.  Laboratory  microtome 31 

4.  Sliding  microtome  of  Jung 33 

5.  Apparatus  for  cutting  tissues  frozen  by  carbon  dioxid      36 

6.  Movements  in  honing 37 

7.  Diagram  of  cell  (Huber) 52 

8.  Cylindric  ciliated  cells  from  the  primitive  kidney  of  Petroniyzon  planeri  ....  53 
9-19.   Processes  of  mitotic  cell-  and  nuclear  division 5&>  $9 

20-27.   Mitotic  cell-division  of  fertilized  whitefish  eggs  (Huber) 60,  61 

28.   Mitotic  division  of  cells  in  testis  of  salamander  (Benda  and  Guenther)    ....  63 

29-34.   Process  of  fertilization  (Boveri) 66,  67 

35.  Pigment  cell  from  the  skin  of  the  head  of  a  pike 71 

36.  Isolated  cells  of  squamous  epithelium  (Huber) 76 

37.  Surface  view  of  squamous  epithelium  from  skin  of  a  frog 76 

38.  Simple  columnar  epithelium  from  the  small  intestine  of  man  (Huber)      ....  77 

39.  Pseudostratified  columnar  epithelium     ....        77 

40.  Stratified  pavement  epithelium .    .  j8 

41.  Cross- section  of  stratified  squamous  epithelium  from  esophagus  of  man  (Huber)  78 

42.  Isolated  transitional  epithelial  cells  from  bladder  of  man  (Huber) 79 

43.  Cross-section  of  transitional  epithelium  from  the  bladder  of  a  young  child  (Huber)  79 

44.  Stratified  columnar  epithelium 80 

45.  Ciliated  cells  from  bronchus  of  dog 80 

46.  Cross-section  of  stratified  ciliated  columnar  epithelium  from  trachea  of  rabbit 

(Huber) ' 80 

47.  Goblet  cells  from  bronchus  of  dog 81 

48.  Simple  tubular  glands 82 

49.  Excretory  ducts  and  lumina  of  the  secretory  portion  of  a  compound  tubular 

gland 83 

50.  Lumina  of  the  secreting  portion  of  a  reticulated  tubular  gland 83 

51.  Glandular  classification 83 

52.  Mesothelium  from  pericardium  of  rabbit  ( Huber) 85 

53.  Mesothelium  from  mesentery  of  rabbit  (Huber) 86 

54.  Mesothelium  from  peritoneum  of  frog 86 

55.  Mesothelium  covering  posterior  abdominal  wall  of  frog  (Huber) 86 

56.  Endothelial  cells  from  small  artery  of  mesentery  of  rabbit  (Huber) 86 

57.  Mesenchymatous  tissue  from  the  subcutis  of  a  duck  embryo  ...        89 

58.  White  fibrils  and  bundles  from  teased  preparation  of  a  fresh  tendon  from  tail  of 

rat  (Huber) 91 

59.  Elastic  fibers  from  ligamentum  nuchse  of  ox 91 

60.  Reticular  connective  tissue  from  lymph-gland  of  man 93 

61.  Areolar  connective  tissue  from  subcutaneous  tissue  of  rat  (Huber) 94 

62.  Cell-spaces  in  the  ground-substance  of  areolar  connective  tissue  of  young  rat 

(Huber) 94 

63.  Connective-tissue  cells  from  pia  mater  of  dog  (Huber)        94 

64.  Pigment  cells  found  on  the  capsule  of  sympathetic  ganglion  of  frog  (Huber)  .    .  95 

65.  Leucocyte  of  frog  with  pseudopodia 95 

66.  Fibrous  connective  tissue  from  great  omentum  of  rabbit 96 

6?.  Longitudinal  section  of  tendon 97 

68.  Cross-section  of  secondary  tendon  bundle  from  tail  of  rat  (Huber) 97 

69.  Tendon  cells  from  tail  of  rat  (Huber)    .  98 

70.  Cross-section  of  ligamentum  nuchoe  of  ox  (Huber) 98 

71.  Fat-cell      99 

II 


12  ILLUSTRATIONS. 

FIG.  PAGE 

72.  Hyaline  cartilage 100 

73.  Section  through  cranial  cartilage  of  squid      100 

74.  Insertion  of  the  ligamentum  teres  into  the  head  of  the  femur 101 

75.  Elastic  cartilage  from  external  ear  of  man 102 

76.  Longitudinal  section  through  a  lamellar  system  (v.  Ebner) 104 

77.  78.   Lamellae  seen  from  the  surface  (v.  Ebner) 104 

79.  Segment  of  a   transversely  ground  section  from  the  shaft  of  a  long  bone, 

showing  lamellar  system  . 105 

80.  Portion  of  a  transversely  ground  disc  from  the  shaft  of  a  human  femur    .    .    .  106 

8 1.  Longitudinal  section  through  a  long  bone  of  a  lizard  embryo 108 

82.  Longitudinal  section  of  the  proximal  end  of  a  long  bone  of  a  sheep  embryo  .  109 

83.  Longitudinal  section  through  area  of  ossification  from  long  bone  of  human 

embryo  (Huber)     .    . no 

84.  Longitudinal  section  through  epiphysis  of  arm  bone  of  sheep  embryo      ...  113 

85.  Section  through  the  lower  jaw  of  an  embryo  sheep 114 

86.  Cross-section  of  developing  bone  from  leg  of  human  embryo,  showing  endo- 

chondral  and  intramembranous  bone  development  (Huber) 115 

87.  Cross-section  of  shaft  (tibia  of  sheep) 116 

88.  Smooth  muscle  from  intestine  of  cat 124 

89.  Cross-section  of  striated  muscle-fibers 125 

90.  Muscle-fiber  from  ocular  muscles  of  rabbit        125 

91.  Striated  muscle-fiber  of  frog,  showing  sarcolemma  (Huber) 125 

92.  Diagram  of  structure  of  fibrils  of  a  striated  muscle-fiber  (Huber) 125 

93.  Transverse  section  through  striated  muscle-fiber  of  rabbit       126 

94.  Diagram  of  transverse  striation  in  the  muscle  of  an  arthropod 127 

95.  Striated  muscle  fiber  of  man 128 

96.  Cross-section  through  the  trapezius  muscle  of  man 128 

97.  Branched,  striated  muscle-fiber  from  tongue  of  frog  (Huber) 129 

98.  Cross-section  of  rectus  abdominis  of  child,  under  low  magnification  (Huber)  .  130 

99.  Longitudinal  section  through  the  line  of  junction  between  muscle  and  tendon  130 
100,  101.   Longitudinal  and  cross-section  of  muscle-fibers  from  the  human  myo- 
cardium                   131 

102.  Bipolar  ganglion  cell  from  the  ganglion  acusticum  of  a  teleost 135 

103.  Chromatophile  granules  of  a  ganglion  cell  from  the  Gasserian  ganglion  of  a 

teleost .    .                 136 

104.  Nerve-cell  from  the  anterior  horn  of  the  spinal  cord  of  an  ox 136 

105.  Motor   neurones   from   anterior   horn   of    the    spinal   cord  of  new-born   cat 

(Huber) 137 

106.  A  nerve-cell  with  branched  dendrites  (Purkinje's  cell),  from  cerebellar  cortex 

of  rabbit 137 

107.  Pyramidal  cell  from  cerebral  cortex  of  man ,    .    .  138 

108.  Nerve-cell  with  dendrites  ending  in  claw-like  telodendria      .    . 139 

109.  Ganglion  cell  with  a  T-shaped  process 139 

no.  Ganglion  cell  from  Gasserian  ganglion  of  rabbit  (Huber) 140 

in.  Ganglion  cells  from  spinal  ganglion  of  rabbit  embryo 140 

112.  Neurone  from  inferior  cervical  sympathetic  ganglion  of  rabbit  (Huber)    .    .    .  141 

113.  Longitudinal  section  of  nerve- fiber    ...             142 

114.  Transverse  section  through  sciatic  nerve  of  frog 143 

115.  Medullated  nerve-fibers  from  rabbit 144 

116.  Remak's  fibers  from  pneumogastric  nerve  of  rabbit 144 

117.  Diagram  to  show  composition  of  a  peripheral  nerve-trunk  (Huber) 146 

118.  Cross-section  through  a  peripheral  nerve 146 

119.  Peripheral  motor  neurone  (Huber) 148 

120.  Motor  nerve-ending  in  voluntary  muscle  of  rabbit  (Huber-De  Witt)     .        .    .  149 
121-125.   Motor  endings  in  striated  voluntary  muscles 150 

126.  Motor  nerve-ending  in  striated  voluntary  muscle  of  frog  (Huber-De  Witt)  .    .  151 

127.  Motor  nerve-ending  on  heart  muscle-cells  of  cat  (Huber-De  Witt)  .    .         .  151 

128.  Motor  nerve-ending  on  involuntary  nonstriated  muscle-cell  from  intestine  of 

cat  (Huber-De  Witt) ' 151 

129.  Peripheral  sensory  neurone  (Huber) 152 

130.  Termination  of  sensory  nerve-fibers  in  the  mucosa  and  epithelium  of  urethra 

of  cat  (Huber)  4 153 

131.  End-bulb  of  Kra'use  from  conjunctiva  of  man  (Dogiel) 154 

132.  Meissner's  tactile  corpuscle  (Dogiel)      155 

133.  Genital  corpuscle  from  glans  penis  of  man  (Dogiel) 156 


ILLUSTRATIONS.  1 3 

FIG.  PAGE 

134.  Cylindric  end-bulb  of  Krause  from  intermuscular  fibrous  tissue  septum  of  cat 

(Huber)                                                                157 

135.  Pacinian  corpuscles  from  mesorectum  of  kitten  (Sala) 158 

136.  Corpuscle  of  Herbst  from  bill  of  duck  ....             159 

137.  Intrafusal  muscle-fiber  from  neuromuscular  nerve  end-organ  of  rabbit  (Huber)  160 

138.  Cross-section  of  a  neuromuscular  nerve  end-organ  from  interosseous  muscle  of 

man  (Huber) .    .    .  160 

139.  Neuromuscular  nerve  end-organ  from  plantar  muscles  of  dog  ( Huber-De  Witt)  161 

140.  Neurotendinous  nerve  end-organ  from  rabbit  (Huber-De  Witt)     .             ...  162 

141.  Cross-section  of  neurotendinous  nerve  end-organ  of  rabbit  (Huber-De  Witt)  .  163 

142.  Ranvier's  crosses  from  sciatic  nerve  of  rabbit        165 

143.  Medullated  nerve-fiber  from  sciatic  nerve  of  frog 165 

144.  Ganglion  cell  from  anterior  horn  of  spinal  cord  of  calf 166 

145.  Human  red  blood-cells                          170 

146.  Rouleau  formation  of  human  erythrocytes 170 

147.  Hemin,  or  Teichmann's  crystals,  from  blood  stains  on  a  cloth  (Huber)    ...  170 

148.  Crenated  human  red  blood-cells                  .        . 170 

149.  Red  blood-corpuscles  subjected  to  the  action  of  water 170 

150.  Red  blood-corpuscles  from  various  vertebrate  animals 171 

151.  White  blood-corpuscles  from  normal  blood  of  man      173 

152.  Ehrlich's  leucocytic  granules 174 

153.  Solitary  lymph-nodule  from  human  colon 178 

154.  Section  through  mesenteric  lymph-gland  of  cat,  with  injected  blood-vessels    .  179 
155-  Section  from  human  lymph-gland  ......        180 

156.  Section  through  the  human  spleen 181 

157.  Lobule  of  the  spleen  (Mall) 183 

158.  Cells  containing  pigment,  blood-corpuscles,  and  hemic  masses  from  spleen  of 

dog 184 

159.  Section  through  human  spleen  showing  reticular  fibrils 184 

1 60.  Cover-glass  preparation  from  bone-marrow  of  dog 1 86 

161.  Section  through  human  red  bone-marrow.             187 

162.  Small  lobule  from  thyinus  of  child,  with  well-developed  cortex 189 

163.  HassalPs  corpuscle  and  a  small  portion  of  medullary  substance  from  thymus  of 

child  ten  days  old  (Huber)           189 

164.  Cross-section  of  human  carotid  artery 194 

165.  Section  through  human  artery,  one  of  the  smaller  of  the  medium-sized    .    .    .  195 

1 66.  Precapillary  vessels  from  mesentery  of  cat  (Huber) 195 

167.  Cross-section  of  human  internal  jugular  vein 196 

168.  Section  of  small  human  vein 197 

169.  Endothelial  cells  of  capillary  and  precapillary  from  mesentery  of  rabbit  (Huber)  198 

170.  Small  artery  from  oral  submucosa  of  cat  with  nerve-terminations      199 

171-  Section  of  a  cell-ball  from  glomus  caroticum  of  man  . 203 

172.  Fibrin  from  laryngeal  vessel  of  child             207 

173.  Section  through  lower  lip  of  man 212 

174.  Longitudinal  section  through  a  human  tooth,  showing  lines  of  Retzius     .    .    .  214 

175.  Portion  of  ground  tooth  from  man,  showing  enamel  and  dentin 215 

176.  Longitudinal  section  through  human    molar  from  the  center  of  the  enamel 

layer 216 

177.  Cross-section  of  human  tooth,  showing  cement  and  dentin 217 

178.  Nerve  termination  in  pulp  of  rabbit's  molar  (Huber)      2l8 

179-182.   Four  stages  in  the  development  of  tooth  in  sheep  embryo 219 

183.  Portion  of  cross-section  through  developing  tooth 22O 

184.  Fungiform  papilla  from  human  tongue  (Huber) 221 

185.  Cross-section  of  human  tongue  showing  filiform  papillae 222 

1 86.  Longitudinal  section  of  foliate  papilla  of  rabbit,  showing  taste-buds  (Huber)  223 

187.  Longitudinal  section  of  a  human  circumvallate  papilla 224 

188.  Schematic  representation  of  a  taste-goblet  (Hermann) 225 

189.  190.   Section  through  tonsil  of  dog 226 

191.  Scheme  of  salivary  gland 227 

192.  Section  through  salivary  gland  of  rabbit,  with  injected  blood-vessels    ....  229 

193.  Section  from  parotid  gland  of  man 230 

194.  Section  of  human  sublingual  gland 230 

195.  Alveoli  from  submaxillary  gland  of  dog  (Huber) 231 

196.  Section  of  esophagus  of  dog           .    .                    234 

197.  Section  of  human  esophagus,  showing  duct  of  mucous  gland 235 


14  ILLUSTRATIONS. 

FIG.  PAGE 

198.  Epithelium  of  human  stomach,  covering  fold  of  mucosa  between  two  gastric 

crypts 237 

199.  Vertical  section  through  fundus  of  human  stomach .  238 

200.  Gastric  glands  from  fundus  of  stomach  of  young  dog  (Huber) 238 

201.  Section  through  junction  of  human  esophagus  and  cardia 239 

202.  Vertical  section  through  human  pylorus 240 

203.  Section  through  human  pylorus .241 

204.  Section  through  fundus  of  human  stomach  in  condition  of  hunger 242 

205.  Section  through  fundus  of  human  stomach  during  digestion  .         ......  242 

206.  Section  through  mucous  membrane  of  human  small  intestine 244 

207.  Longitudinal  section  through  summit  of  villus  from  human  small  intestine  .    .  245 

208.  Section  through  the  junction  of  the  human  pylorus  and  duodenum 247 

209.  Section  of  solitary  lymph-nodule  from  vermiform  appendix  of  guinea-pig    .    .  248 

210.  Section  through  colon  of  man,  showing  glands  of  Lieberkiihn 249 

211.  Solitary  lymph -follicle  from  human  colon              250 

212.  Section  through  fundus  of  injected  cat's  stomach     .    .                 251 

213.  Schematic  transverse  section  of  human  small  intestine  (Mall) 253 

214.  Portion  of  the  plexus  of  Auerbach  from  stomach  of  cat  (Huber) 254 

215.  Section  of  esophagus  of  cat  showing  nerve-terminations  (Huber) 255 

2lb.    Section  through  liver  of  pig,  showing  chains  of  liver-cells 257 

217.  Section  through  injected  liver  of  rabbit 258 

218,  219.    Human  bile  capillaries 259 

220. -Diagram  of  hepatic  cord  in  transverse  section      260 

221.  Section  through  the  human  liver,  showing  the  beginning  of  bile-ducts     .    .    .  260 

222.  Injected  blood-vessels  in  liver  lobule  of  rabbit 261 

223.  Reticulum  of  dog's  liver 262 

224.  Connective  tissue  from  liver  of  sturgeon,  showing  reticulum .  263 

225.  Section  through  liver  lobule  from  dog,  showing  stellate  cells 264 

226.  Transverse  section  through  alveolus  of  frog's  pancreas 265 

227.  228.   Section  through  human  pancreas 266,  267 

229.  Relation  of  three  adjoining  alveoli  to  excretory  duct,  illustrating  origin  of 

centro-acinal  cells      268 

230.  Section  of  human   pancreas,   showing  gland  alveoli  surrounding  an  area  of 

Langerhans  (Huber) 268 

231.  Vertical. section  through  mucous  membrane  of  human  larynx 275 

232.  Longitudinal  section  of  human  trachea  (Huber)  . 277 

233.  Transverse  section  through  human  bronchus 278 

234»  235-   Sections  of  cat's  lungs 279 

236.  Internal  surface  of  human  respiratory  bronchiole  (Kolliker)       ....             .  280 

237.  Inner  surface  of  human  alveolus,  showing  respiratory  epithelium  (Kolliker)   .  281 

238.  Respiratory  epithelium  in  amphibia 282 

239.  Section  of  human  lung,  showing  elastic  fibers  (Huber) 283 

240.  Section  through  injected  rabbit's  lung 283 

241.  Section  through  thyroid  gland  of  child .  284 

242.  Section  from  parathyroid  of  man  (Huber) 286 

243.  Kidney  of  new-born  infant 287 

244.  Isolated  uriniferous  tubules 288 

245.  Median  longitudinal  section  of  adult  human  kidney 289 

246.  Section  of  cortical  substance  of  human  kidney 290 

247.  Section  of  proximal  convoluted  tubules  from  man 291 

248.  Epithelium  from  proximal  convoluted  tubule  of  guinea-pig,  with  surface  and 

lateral  views  ....        292 

249.  Cortical  portion  of  longitudinal  section  of  kidney  of  child  (Huber) 292 

250.  Section  of  medulla  of  human  kidney 293 

251.  Longitudinal  section  through  papilla  of  injected  kidney 294 

252.  Section  through  junction  of  two  lobules  of  kidney 295 

253.  Diagrammatic  scheme  of  uriniferous  tubules  and  blood-vessels  of  kidney     .    .  297 

254.  Direct  anastomosis  between  an  artery  and  vein  in  a  column  of  Bertini  of  child  298 
255-   Section  of  lower  part  of  human  ureter 300 

256.  Section  of  suprarenal  cortex  of  dog       302 

257.  Arrangement  of  intrinsic  blood-vessels  in  cortex  and  medulla  of  dog's  adrenal 

(Flint) 303 

258.  Section  from  ovary  of  adult  dog  (Waldeyer) 307 

259.  Section  from  ovary  of  young  girl 308 

260-263.   Sections  from  cat's  ovary 310 


ILLUSTRATIONS.  1 5 

FIG.  PAGE 

264.  Representation  of  behavior  of   the  chromatin  during  the  maturation  of  the 

ovum  (Ruckert) 312 

265.  Scheme  of  the  development  and  maturation  of  an  ascaris  ovum  (Boveri)     .    .  314 

266.  Section  of  fully  developed  Graafian  follicle  from  pig 315 

267.  Section  of  oviduct  of  young  woman 317 

268.  Section  from  uterus  of  young  woman 319 

269.  Section  of  human  vagina  (Huber) 320 

270.  Section  of  human  labia  minora  (Huber) 321 

271.  Diagram  showing  characteristics  of  spermatozoa  of  vertebrates 323 

272.  Human  spermatozoa 324 

273.  Longitudinal  section  through  human  testis  and  epididymis 325 

274.  275.   Sustentacular  cells 326 

276.  Section  of  human  testis  (Huber) 327 

277.  Section  through  human  vasa  efferentia 328 

278.  Cross-section  of  vas  epididymidis  of  human  testis  (Huber) 328 

279.  Section  of  dog's  testis  with  injected  blood-vessels    ....        329 

280.  Cross-section  of  vas  deferens  near  epididymis  (human)  (Huber) 330 

281.  Cross-section  of  wall  of  seminal  vesicle  (human)  (Huber) 331 

282.  Section  of  prostate  gland  of  man  (Huber) 331 

283.  Schematic  diagram  of  spermatogenesis  as  it  occurs  in  ascaris  (Boveri)  ....  335 

284.  Schematic  diagram  of    section    through  convoluted  seminiferous   tubule   of 

mammal  (Hermann)      337 

285.  Section  of  convoluted  tubule  from  rat's  testicle 338 

286.  Under  surface  of  the  epidermis  ....        342 

287.  Cross-section  of  skin  of  child  with  injected  blood-vessels 343 

288.  Prickle  cells  from  the  stratum  Malpighii  of  man 344 

289.  Cross-section  of  human  epidermis 345 

290.  Cross-section  of  negro's  skin 346 

291.  Nerves  of  epidermis  and  papillae  from  ball  of  cat's  foot 348 

292.  293.   Meissner's  corpuscle  from  man 349 

294.  Grandry's  corpuscles  from  duck's  bill 350 

295.  Longitudinal  section  of  human  hair  and  follicle 352 

296.  Cross-section  of  human  hair  with  follicle 353 

297.  Longitudinal  section  of  cat's  hair  and  follicle,  showing  nerve-termination    .    .  354 

298.  Longitudinal  section  through  human  nail  and  its  groove 355 

299.  Transverse  section  through  human  nail  and  its  sulcus '.    .    .  356 

300.  Cross-section  of  coiled  tubule  of  sweat-glands  from  human  axilla 357 

301.  Tangential  section  through  coiled  tubule  of  sweat-glands  from  human  axilla  .  357 

302.  Section  of  alveoli  from  sebaceous  gland  of  human  scalp  (Huber) 359 

303.  Section  of  mammary  gland  of  nullipara  (Nagel) 360 

304.  Transverse  section  through  human  skin 363 

305.  Cross-sections  of  human  spinal  cord 366 

306.  Schematic  diagram  of  spinal  cord  in  cross-section  (von  Lenhossek)     ....  368 

307.  Schematic  cross-section  of  spinal  cord  (Ziehen) 369 

308.  Section  through  human  cerebellar  cortex  vertical  to  the  surface  of  the  convolution  372 

309.  Schematic  diagram  of  cerebellar  cortex 373 

310.  Cell  of  Purkinje  from  human  cerebellar  cortex 374 

311.  Granular  cell  from  the  granular  layer  of  the  human  cerebellar  cortex  .    .    .    .  374 

312.  Schematic  diagram  of  cerebral  cortex 377 

313.  Large  pyramidal  cell  from  human  cerebral  cortex 377 

314.  Schematic  diagram  of  cerebral  cortex 378 

315.  Olfactory  bulb 380 

316.  Longitudinal  section  of  spinal  ganglion  of  cat  (Huber)      382 

317.  Ganglion  cell  from  the  Gasserian  ganglion  of  a  rabbit  (Huber) 383 

318.  Diagram  showing  the  relations  of  the  neurones  of  a  spinal  ganglion  (Dogiel)  384 

319.  Neurone  from  inferior  cervical  sympathetic  ganglion  of  a  rabbit  (Huber)     .    .  385 

320.  From  section  of  semilunar  ganglion  of  cat  ( Huber) 386 

321.  From  section  of  stellate  ganglion  of  dog  (Huber) 3^7 

322.  From  section  of  sympathetic  ganglion  of  turtle  (Huber) 388 

323.  From  section  of  sympathetic  ganglion  of  frog  (Huber) 388 

324.  Schematic  diagram  of  a  sensorimotor  reflex  arc  according  to  the  modern  neu- 

rone theory 389 

325.  Schematic  diagram  of  a  sensorimotor  reflex  cycle 390 

326.  Schematic  diagram  of  the  reflex  tracts  between  a  peripheral  organ  and  the 

brain  cortex 391 


1 6  ILLUSTRATIONS. 

FIG.  PAGE 

327.  Neurogliar  cells  (Huber) 392 

328.  Section  through  injected  cerebral  cortex  of  rabbit 395 

329.  Schematic  diagram  of  the  eye  (Leber  and  Flemming) .  408 

330.  Section  through  the  anterior  portion  of  human  cornea 410 

331.  Corneal  spaces  of  dog 411 

332.  Section  through  the  human  choroid 413 

333.  Meridional  section  of  the  human  ciliary  body 415 

334.  Injected  blood-vessels  of  the  human  choroid  and  iris .  417 

335.  Section  of  the  human  retina 419 

336.  Section  through  point  of  entrance  of  human  optic  nerve 421 

337.  Section  through  human  macula  lutea  and  fovea  centralis 421 

338.  Schematic  diagram  of  the  retina  (Ramon  y  Cajal) 424 

339.  Injected  blood-vessels  of  the  human  retina 426 

340.  Injected  blood-vessels  of  human  macula  lutea 426 

341.  Cross-section  of  upper  eyelid  of  man 431 

342.  Schematic  representation  of  the  complete  auditory  apparatus  (Schwalbe)     .    .  436 

343.  Cross-section  of  the  Eustachian  tube 438 

344.  Right  bony  labyrinth  (Quain,  after  Sommering) 439 

345.  Membranous    labyrinth   from   five-month   human   embryo    (Schwalbe,    after 

Retzius) 440 

346.  Transverse  section  through  an  osseous  and  membranous  semicircular  canal  of 

an  adult  human  being 441 

347.  Vertical  section  through  the  anterior  ampulla 443 

348.  Section  through  a  turn  of  the  osseous  and  membranous  cochlear  duct  of  the 

cochlea  of  guinea-pig 445 

349.  Organ  of  Corti  (Retzius) 448 

350.  Surface  of  organ  of  Corti,  with  surrounding  structures  (Retzius) 451 

351.  Scheme  of  distribution  of  blood-vessels  in  labyrinth  (Eichler) 453 


INTRODUCTION   TO   MICROSCOPIC 
TECHNIC. 

L    THE  MICROSCOPE  AND  ITS  ACCESSORIES. 

A  detailed  description  of  the  microscope  and  its  accessory  appa- 
ratus hardly  lies  within  the  scope  of  this  book.  If,  notwithstanding, 
a  few  points  be  touched  upon,  it  is  done  only  that  the  beginner 
may  have  a  working  knowledge  of  the  different  parts  of  the  instru- 
ment which  he  must  use.  A  more  intimate  knowledge  of  the  theory 
of  the  microscope  may  be  acquired  by  studying  such  works  as 
those  of  Dippel,  A.  Zimmermann,  and  Carpenter. 

1.  Histologic  specimens  are  examined  with  the  aid  of  the  micro- 
scope, an  instrument  which  magnifies  the  objects  by  means  of  its 
optic  apparatus.      For  this  purpose  simple  microscopes,  consisting 
usually  of  a  single  lens,  are  not  sufficient ;  the  aid  of  the  compound 
microscope,  which  contains  a  combination  of  two  systems  of  lenses, 
is  necessary.     These  systems  may  be   changed  according  to  the 
needs  of  the  case,  and  thus  a  variation  in  the  magnification  of  the 
object  obtained.      The  rest  of  the  instrument  consists  of  a  frame- 
work called  the  stand,  the  lower  portion  of  which  consists  of  afoot- 
plate  or  base,  which  should  rest  firmly  on  the  table.      From  the 
base  rises  the  column  or  pillar,  to  which  the  other  parts  of  the 
microscope  are  attached.      From  below  upward  come  the  movable 
mirror,  the  stage  and  substage  with  diaphragm  and  condenser,  and 
the  tube  with  pinion  and  fine  adjustment. 

One  side  of  the  mirror  is  concave,  and  serves  to  concentrate  the 
rays  of  light  in  the  direction  of  a  central  opening  in  the  stage.  The 
other  side  is  plane,  and  is  seldom  used.  If  the  objects  are  to  be  ex- 
amined by  direct  illumination,  and  not  by  transmitted  light,  the 
mirror  is  so  placed  that  the  rays  are  reflected  away  from  the  open- 
ing in  the  stage. 

2.  The  specimen  to  be  examined  is  placed  on  the  stage,  over 
the  central  opening.      If  the  light  be  too  strong,  the  opening  may 
be  diminished  in  size  by  means  of  a  diaphragm.      In  some  instru- 
ments these  diaphragms  are  placed  in  the  opening  of  the  stage,  and 
consist  of  plates  with  different  sized  apertures.     A  better  form  is 
composed  of  one  large  disc  containing  several  apertures  of  different 
sizes.     This  is  fastened  to  the  under  surface  of  the  stage  in  such  a 
way  that  by  revolving  the  disc  the  apertures  may  be  brought  one 

2  I7 


i8 


THE    MICROSCOPE    AND    ITS    ACCESSORIES. 


after  the  other  opposite  the  opening  in  the  stage.  A  much  better 
diaphragm,  constructed  on  an  entirely  different  principle,  is  the  so- 
called  iris  diaphragm.  Although  its  opening  is  not  exactly  circu- 
lar, yet  it  has  the  advantage  of  being  easily  enlarged  or  contracted 
by  manipulating  a  small  handle  controlling  the  metal  plates  sliding 
over  one  another. 

3.  The  tube,  which  is  contained  in  a  close-fitting  metal  sheath, 
is  attached  to  the  upright  of  the  microscope.      In  the  simpler  forms 


Ocular  or  eyepiece. 


Draw-tube. 


Tube. 


Triple  nose-piece. 
Objectives. 


Stage.   — 


Iris  diaphragm  and 
Abbe  condenser. 


Screw  for  focusing 
condenser. 


Mirror.  _ 


Rack  and  pinion  for 
•  coarse  adjustment. 


Micrometer  screw  for 
fine  adjustment. 


Pillar. 


-  Stand. 


Fig.  I. — Microscope. 


of  microscopes  the  tube  is  raised,  lowered,  or  twisted  by  hand.  In 
more  complicated  instruments  the  upward  and  downward  move- 
ments are  accomplished  by  means  of  a  rack  and  pinion — coarse 
adjustment.  A  micrometer  screw — fine  adjustment — situated 
at  either  the  upper  or  the  lower  end  of  the  upright,  controls  the  fine 
adjustment.  The  tube  possesses  an  upper  and  a  lower  opening,  into 
which  lenses  may  be  laid  and  screwed. 

4.  The  ocular,  into  the  ends  of  which  lenses  are  inserted,  fits  into 


LENSES.  1 9 

the  upper  opening.  The  upper  is  called  the  ocular  lens,  the  lower 
the  collective  lens.  The  objective  system,  which  is  a  combination 
of  several  lenses,  the  lowest  and  smallest  of  which  is  known  as  the 
front  lens,  is  screwed  into  the  lower  opening  of  the  tube. 

5.  All  larger  instruments   possess   several  oculars   and  objec- 
tives, which  together  give  different  magnifications  according  to  the 
combinations  used.      For  most  objects  a  magnification  of  500  diam- 
eters  is  all   that  is   required,  but   to   obtain  this  and  still  have  a 
clear  and  bright  field  the  ordinary  lenses  are  hardly  sufficient.     The 
greater  the  magnification,  the  darker  is  the  field.     To  avoid  this, 
illuminating  mechanisms  (condensers,  Abbe's  apparatus)  have  been 
constructed,  by  means  of  which  the  rays  of  light  are  concentrated 
and  controlled.     This  arrangement  is  absolutely  necessary  for  deli- 
cate work. 

6.  Even  with  the  aid  of  such  an  apparatus  the  dry  objective  sys- 
tems are  not  sufficient.     With  them  the  rays  of  light  must  pass 
through  different  media  having  various  indices  of  refraction.     The 
rays  pass  from  the  object  through  the  cover-slip,  and  then  through 
the  air  between  the  latter  and  the  objective  system.     They  are  thus 
deflected  in  different  directions — a  defect  which  would  be  avoided 
if  the  rays  were  made  to  pass  through  a  single  medium.     This  latter 
condition  may  be  practically  brought  about  by  placing  between  the 
objective  and  the  cover-glass  a  drop  of  some  fluid  having  about  the 
same  refractive  index  as  the  glass.     The  lens  is  then  lowered  into 
the  fluid.     As  this  invention  has  proved  useful,  so-called  immersion 
lenses  have  been  made  during  recent  years. 

7.  There  are  thus  two  kinds  of  lens  systems — the  dry  and  the 
immersion  lenses.     The  latter  are  divided  into  two  groups — lenses 
with  water  and  those  with  oil  immersion.      As  oil  has  a  greater 
index  of  refraction  than  water,  and  one  more  nearly  approaching 
that  of  glass,  the  oil-immersion  lenses  are  at  present  the  best  objec- 
tives that  we  possess.      Karl  Zeiss,  of  Jena,  and  other  microscope 
makers,  have  in  late  years  made  lenses  from  a  special  sort  of  glass 
which  reduces  to  a  minimum  the  chromatic  and  spheric  aberration 
of  the  rays  of  light  in  their  passage  through  the  objective  (apochro- 
matic  lenses). 

8.  The  rays  of  light   reflected   from   the    mirror  and  passing 
through  the  object  are  refracted  by  the  objective  system  in  such  a 
way  that  they  are  focused  in  a  so-called  real  image  at  a  point  about 
half-way  up  the  tube.      This  picture  is  an  inverted  one,  the  right 
side  of  the  microscopic  field  being  at  the  left  of  the  real  image,  and 
the  upper  portion  below.     The  picture  is,  in  other  words,  rotated 
1 80  degrees.      By  means  of  the  ocular  the  real  image  is  again  mag- 
nified— virtual  image — but  no  longer  inverted,  although  to  the  eye 
of  the  microscopist  the  field  actually  appears  inverted.     To  shut  out 
the   rays   of  light,  which  cause  a  diffused  picture,  diaphragms  are 
sometimes  introduced  into  the  tube  as  well  as  into  the  ocular. 

9.  The  objects  to  be  examined  are  placed  upon  a  glass  plate 


2O  THE    MICROSCOPIC    PREPARATION. 

called  a  slide.  Microscopic  slides  are  of  different  sizes,  and  are 
usually  oblong  in  shape.  Those  in  most  common  use  are  three 
inches  long  and  an  inch  wide.  The  object  is  covered  by  a  very 
much  smaller  and  thinner  glass  plate — the  cover=slip.  The  whole 
preparation  is  then  placed  upon  the  stage,  in  such  a  way  that  the 
cover-slip  is  upward  and  immediately  beneath  the  end  of  the  tube. 
The  mirror  of  the  microscope  is  now  so  adjusted  as  to  concentrate 
the  rays  of  light  on  the  preparation,  illuminating  it  as  much  as  is 
necessary.  By.  means  of  the  rack  and  pinion,  or  coarse  adjustment, 
the  whole  tube  is  now  slowly  lowered  toward  the  cover- slip  until 
the  bare  outlines  of  the  object  are  dimly  seen  in  the  white  field. 
From  this  point  on,  the  micrometer  screw,  or  fine  adjustment,  is  used 
in  bringing  the  front  lens  down  to  its  proper  focal  distance  from  the 
preparation.  The  object  is  now  seen  to  be  clear  and  well  defined. 
By  turning  the  screw  to  the  right  or  the  left,  different  parts  of  the 
specimen  are  brought  more  clearly  into  view,  this  result  being  due 
to  the  fact  that  not  all  points  in  the  preparation  are  in  the  same 
plane. 

10.  In  studying  objects  it  is  always  well  to  draw  them,  using  a 
sharpened  pencil  and  smooth  paper.  The  beginner  soon  finds  that 
with  constant  practice  he  can  sketch  the  different  parts  of  the  field 
in  nearly  their  proper  relationship.  This  by  no  means  easy  work  is 
facilitated  by  the  use  of  a  drawing  apparatus  called  the  camera 
lucida.  The  best  of  these  is  that  devised  by  Abbe.  It  is  fastened 
to  the  upper  end  of  the  tube,  above  the  ocular.  The  apparatus  is  so 
made  that  both  the  preparation  and  the  drawing  surface  are  seen  by 
the  same  eye.  The  microscopic  field  is  seen  directly,  while  the  draw- 
ing surface  is  made  visible  by  means  of  a  mirror.  When  the  appa- 
ratus is  in  place  and  the  drawing  commenced,  it  appears  to  the  one 
sketching  as  if  his  pencil  were  moving  over  the  preparation  itself. 
Outlines  are  reproduced  on  paper  with  great  exactness  both  as 
to  form  and  size ;  finer  details  must  of  course  be  sketched  in  free 
hand. 

Every  preparation  should  first  be  examined  with  a  low  power, 
and  only  after  the  student  has  studied  the  specimen  as  a  whole  and 
found  instructive  areas  should  the  higher  powers  be  used. 


IL  THE  MICROSCOPIC  PREPARATION* 

11.  In  many  cases  the  making  of  a  microscopic  preparation  is  a  very 
simple  procedure,  especially  when  fresh  objects  are  to  be  examined.     A 
drop  of  blood,  for  instance,  may  simply  be  placed  upon  a  slide,  covered 
with  a  cover-slip,  and  examined.      Other  objects,  as  the  mesentery,  thin 
transparent  nerves,  detached  epithelia,  spermatozoa,  etc.,  need  no  further 
preparation,  but  may  be  examined  at  once. 

12.  Portions  of  larger  organs  are    often  studied  after  having  been 
teased,  which  may  be  done  by  means  of  two  needles  fastened  in  handles. 
If  the  objects  be  composed  of  fibers  running  in  parallel  directions,  one 


SECTIONS    OF    FRESH    TISSUES.  21 

needle  is  thrust  into  the  substance  to  hold  it  in  place,  while  the  other  is 
used  to  tear  the  fibers  apart.  This  method  is  used  in  examining  muscles, 
nerves,  tendons,  etc. 

Some  tissues  are  so  constituted  that  they  can  only  be  investigated  by 
means  of  sections,  which  permit  a  study  of  their  elements  and  the  rela- 
tionship of  the  same  to  each  other.  In  this  method  an  ordinary  razor, 
moistened  in  some  fluid,  may  be  employed.  As  a  rule,  it  is  not  the  size 
of  the  section,  but  the  thinness,  which  is  important.  This  latter  is 
obtained  only  by  practice.  Every  microscopist  ought  to  become  accus- 
tomed to  making  free-hand  sections  with  the  razor.  It  is  the  simplest  of 
all  methods,  is  very  rapid,  and  is  especially  useful  in  the  quick  identifica- 
tion of  a  tissue.  In  cutting  fresh  so-called  parenchymatous  tissues,  such 
as  liver  and  kidney,  an  ordinary  razor  is  not  sufficient.  Here  a  double 
knife  is  necessary.  This  consists  of  two  blades,  which  are  so  placed  one 
above  the  other  that  their  distal  ends  touch,  while  their  proximal  ends 
are  slightly  separated.  The  distance  of  the  blades  from  each  other  is 
regulated  by  a  screw.  If  this  be  removed  the  knives  may  be  separated 
for  cleaning.  In  making  sections,  only  those  portions  of  the  blades 
are  of  importance  which  are  very  close  together  but  do  not  actually 
touch.  Sections  are  cut  by  drawing  the  moistened  instrument  quickly 
through  an  organ,  as,  for  instance,  a  fresh  liver.  As  the  organ  is  cut  in 
two,  a  very  thin  section  of  the  tissue  remains  between  the  blades.  This 
is  removed  by  taking  out  the  screw  and  separating  the  blades  in  normal 
salt  solution.  Organs  of  a  similar  consistence  can  be  frozen  and  then  cut 
with  an  ordinary  razor  the  blade  of  which  has  been  cooled.  Sometimes 
good  results  may  be  obtained  by  drying  small  pieces  of  tissue,  as,  for 
instance,  tendon. 

13.  As  sections  or  small  pieces  of  fresh  tissue  would  soon  become 
dry  when  placed  on  the  slide,  they  must  be  kept  moist  during  examina- 
tion.    They   are   therefore  mounted  in  so-called  indifferent    fluids 
(placed  on  the  slide  and  immersed  in  a  few  drops  of  the  indifferent  fluid 
and  covered  with  a  cover-slip).     These  have  the  power  of  preserving  even 
living  organs  for  some  time  without  change.     Such  fluids,  for  instance,  are 
the  lymph,  the  aqueous  humor,  serous  fluids,  amniotic  fluid,  etc.     Artifi- 
cial indifferent  fluids  are  much  used  and  should  always  be  kept  in  stock. 
Of  this  class,  the  following  are  useful : 

1.  Physiologic   saline  solution:     A  0.75%   solution  of  sodium 
chlorid  in  distilled  water. 

2.  Schultze's  iodized  serum:     A  saturated  solution  of  iodin  or 
tincture  of  iodin  in  amniotic  fluid. 

3.  Ranvier's  solution  of  iodin  and  potassium   iodid  :     A  satu- 
rated solution  of  iodin  in  a  2  %  solution  of  potassium  iodid. 

4.  Kronecker' s  fluid  :      Distilled  water,  1000  c.c.;  sodium  chlorid, 
6  gm.  ;  sodium  carbonate,  0.06  gm. 

5.  Solution  of  Ripart  and  Petit :     Copper  chlorid,  0.3  gm.  ;  cop- 
per acetate,   0.3  gm.  ;  aqua  camphorae,  75   c.c.  ;  distilled  water, 
75  c.c.  ;  and  glacial  acetic  acid,  i  c.c.     After  mixing,  this  solution 
is  yellow,  but  clears  up  within  a  few  hours,  and  should  then  be 
filtered. 

14.  The  examination  of  fresh  tissues  comes  far  from  revealing  all  the 
finer  details  of  their  structure.     This  is  partly  due  to  the  fact  that  the 
indices  of  refraction  of  the  different  elements  of  the  tissues  are  too  nearly 


22  THE    MICROSCOPIC    PREPARATION. 

alike,  in  consequence  of  which  the  outlines  are  somewhat  dimmed ;  and 
also,  that  changes  occur,  even  during  the  most  careful  manipulation  of 
the  tissues,  which  result  in  pictures  somewhat  different  from  the  normal. 
These  difficulties  may  be  lessened  by  the  use  of  fixing  fluids.  By 
these  we  mean  those  reagents  which  we  know  by  experience  possess  the 
power  of  preserving  entirely  fresh  (living)  tissues  or  organs  in  such  a  way 
that  accurate  conclusions  as  to  their  condition  and  qualities  during  life 
may  be  obtained.  Even  this  can  be  attained  only  after  a  careful  series 
of  control  observations.  In  general,  fixing  fluids  act  differently  on  dif- 
ferent tissues,  some  preserving  better  one  set  of  elements,  while  others 
give  better  results  with  another  set.  It  is  therefore  always  advisable  to 
fix  in  different  fluids  pieces  of  the  tissues  or  organs  to  be  examined, 

A.  FIXING  METHODS. 

The  fixing  fluids  most  used  for  general  purposes  are  the  following : 

15.  Alcohol. — The  most  common  fixing  fluid  is  alcohol.      It  is  at 
the  same  time  a  hardening  fluid,  as  the  water  of  the  tissues  is  withdrawn 
and  their  albumin  coagulated.      Small  or  thin  pieces  are  put  immediately 
into  absolute  alcohol,  in  which  they  remain  for  from  twelve  to  twenty- 
four  hours.     The  period  required  for  fixation  may  be  greatly  shortened 
by  changing  the  absolute  alcohol  at  the  end  of  one  or  two  hours.     In 
the  case  of  larger  pieces,  a  successive  immersion  in  gradually  increasing 
strengths  of  alcohol  (50%,  70%,  90%)  is  the  method  chosen.     Pieces 
i  c.c.   in  size  remain  for  twenty-four  hours  in  each  grade  of  alcohol, 
larger  pieces  for  a  proportionately  longer  time.     Alcohol  used  in  this  way 
is  a  hardening  fluid  rather  than  a  fixing  fluid. 

16.  Osmic  acid  is  a  reagent  that  kills  quickly,  fixes   exceedingly 
well,  and  even  colors  certain  tissues.     Only  small  pieces  can  be  fixed  in 
this  fluid,  as  it  does  not  easily  penetrate  the  tissues.     It  is  ordinarily  used 
in  a  i  °/0  aqueous  solution,  the  objects  remaining  immersed  twenty-four 
hours.     They  are  then  washed  in  running  water  for  the  same  length  of 
time,    after   which    they   are    transferred  to  90%   alcohol.     Very  small 
objects  may  be  treated  with  osmic  acid  in  the  form  of  vapor  (vaporiza- 
tion).    This  is  done  as  follows  :   A  very  small  quantity  of  osmic  acid  so- 
lution is  put  in  a  small  dish.     The  object  is  then  suspended  by  a  thread 
in  such  a  way  that  it  does  not  come  in  contact  with  the  fluid.     The  dish 
should  be  covered  with  a  well -fitting  lid. 

17.  Flemming's  Solution. — A  solution  with  a  similar  action,  but 
fixing  nuclear  structures  even  better  than  osmic  acid,  is  the  chromic- 
osmic-acetic  acid  solution  of  Flemming  (82)  : 

Osmic  acid,  I  %  aqueous  solution  .    .  lo  parts. 

Chromic  acid,  I  °/0  aqueous  solution  ...  25  " 
Glacial  acetic  acid,  i%  aqueous  solution  .10  " 
Distilled  water 55  " 

Small  pieces  are  fixed  in  a  small  quantity  of  the  fluid  for  at  least 
twenty- four  hours,  sometimes  for  a  longer  period,  extending  even  to 
weeks.  They  are  then  washed  for  twenty-four  hours  in  running  water  and 
passed  through  70%  and  80%,  each  twenty-four  hours,  into  90%  alco- 
hol. 

Flemming  (84)  also  recommends  a  stronger  solution,  which  is  made 
as  follows : 


FIXING    METHODS.  23 

Osmic  acid,  2%  aqueous  solution     ....    4  parts. 
Chromic  acid,  I  %  aqueous  solution    ...15     " 
Glacial  acetic  acid I  part. 

FoPs  Solution. — Fol  has  recommended  the  following  modification 
of  Flemming's  solution  : 

Osmic  acid,  I  c/0  aqueous  solution     ....    2  parts. 
Chromic  acid,  \c/0  aqueous  solution     ...  25     " 
Glacial  acetic  acid,  2C/C  aqueous  solution    .5     " 
Distilled  water 68     " 

In  fixing  with  osmic  acid  and  its  mixtures  it  is  always  advisable  to 
transfer  the  objects  from  water  into  a  weak  alcohol  (50%),  as  by  this 
means  the  shrinking  and  tearing  of  the  tissues  which  sometimes  occur  on 
account  of  the  too  rapid  diffusion  between  the  water  and  alcohol  are 
avoided. 

18.  Hermann's  Solution. — Very  good  results  sometimes  follow  the 
use  of  the  platinum -acetic-osmic  acid  solution  of  Hermann  (89,  i).     It 
is  employed  as  is  Flemming's  solution  : 

Osmic  acid,  2^  aqueous  solution    ....    4  parts. 
Platinum  chlorid,  I  cfo  aqueous  solution  .    .15     " 
Glacial  acetic  acid ...     I  part. 

After  fixing  with  this  solution,  Flemming's  solution,  or  any  other 
osmic  mixture,  the  subsequent  treatment  with  alcohol  may  be  followed 
by  crude  pyroligneous  acid.  The  objects  are  placed  for  from  twelve  to 
twenty-four  hours  in  the  latter  and  then  again  immersed  in  alcohol.  The 
result  is  a  peculiar  coloring  of  the  specimen  which  often  makes  subsequent 
staining  (see  below)  unnecessary  (Hermann). 

19.  Corrosive  Sublimate. — An  excellent  fixing  fluid  is  made  by 
saturating  distilled  water  or  a  physiologic  saline  solution  (see  p.  21)  with 
corrosive  sublimate ;   saline  solutions  keep  better.      Small  pieces,  about 
0.5  cm.  in  diameter,  are  immersed  in  this  fluid  for  from  three  to  twenty- 
four  hours,  are  then  washed  in  running  water  for  twenty-four  hours,  and 
then  transferred  into  70%  alcohol.     After  twenty-four  hours  the  tissues  are 
placed  in  80%  for  the  same  length  of  time,  and  then  preserved  in  90% 
alcohol.      It  often  occurs  that  after  changes  in  temperature  crystals  of  sub- 
limate are  formed  on  the  surface  or  in  the  interior  of  the  object.      For 
their  removal  a  few  drops  of  a  solution  of  iodin  and  potassium  iodid  are 
added  to  the  alcohol  (P.   Mayer,  87).     It  is  a  matter  of  indifference 
whether  the  70%,  80%   or  90%  alcohol  is  thus  iodized.     In  the  further 
treatment  of  the  object,  as  well  as  in  sectioning,  any  such  crystals  of  sub- 
limate will  not  be  found  to  be  a  hindrance.     Indeed,  in  the  case  of  very 
delicate  objects  it  is   often  more  advantageous  to  undertake  their  removal 
after  sectioning  by  adding  iodin  to  the  absolute  alcohol  then  used. 

20.  Picric  Acid. — Small  and  medium-sized  objects  (up  to  i  c.c.) 
are  fixed  in  twenty-four  hours  in  a  saturated  aqueous  solution  of  picric 
acid  (about  0.75%),   although    an  immersion    lasting  for  weeks  is  not 
detrimental,  especially  if  the  objects  be  of  considerable  size.     The  tissues 
are  transferred  to  70%  or  80%  alcohol,  in  which  they  remain  until  the 
alcohol  is  not  colored  by  the  picric  acid.     They  are  then  preserved  in 
90%  alcohol. 

21 .  Instead  of  a  pure  solution  of  picric  acid,  the  picrosulphuric  acid 
of  Kleinenberg  or  the  picric-nitric  acid  of  P.  Mayer  (81)  may  be  used. 


24  THE    MICROSCOPIC    PREPARATION. 

The  first  is  made  thus:  i  c.c.  of  concentrated  sulphuric  acid  is  added 
to  100  c.c.  of  a  saturated  aqueous  picric  acid  solution.  This  is  allowed 
to  stand  for  twenty-four  hours,  then  filtered,  and  diluted  with  double  its 
volume  of  distilled  water.  The  picric -nitric  acid  solution  is  made  by 
adding  2  c.c.  of  pure  nitric  acid  to  100  c.c.  of  a  saturated  picric  acid 
solution.  Filter  after  standing  for  twenty-four  hours. 

22.  Rabl's  Solutions. — C.   Rabl  (94)   recommends  the  following 
mixtures,  especially  for  embryos  :     ( i )  Concentrated  aqueous  solution  of 
corrosive    sublimate,    i    vol.  ;    concentrated  aqueous   solution    of  picric 
acid,  i  vol.  ;  distilled  water,  2  vols.      (2)    i   per  cent,   aqueous  solution 
of  platinum  chlorid,  i  vol.  ;  concentrated  aqueous  solution  of  corrosive 
sublimate,    i   vol.  ;    distilled  water,  2  vols.      In  both  cases,   after  being 
washed  twelve  hours  in  water  (in  the  first  preferably  in  alcohol)   the 
specimens  are  transferred  to  gradually  increased  strengths  of  alcohol. 

23.  Acetic  Sublimate  Solution. — This  is  an  excellent  fluid,  and  at 
present  much  used  for  embryonic  tissues  and  for  organs  containing  only  a 
small  quantity  of  connective  tissue.     To  a  saturated  aqueous  solution  of 
sublimate,  5%  to  10%  of  glacial  acetic  acid  is  added.     After  remaining 
two  or  three  hours  or  more  in  this  solution,  the  objects  are  transferred  to 
35%  alcohol,  after  which  they  are  passed  through  the  higher  grades. 

24.  O.  vom  Rath  (95)  recommends,  among  others,  the  following  two 
solutions:      (i)  Picric=osmic=acetic acid  solution.     Add  to  1000  c.c. 
of  a  cold  saturated  picric  acid  solution  i  gm.  of  osmic  acid,  and  after 
several  hours  4  c.c.  of  glacial  acetic  acid.      Objects  are  fixed,  according 
to  their  size,  in  four,  fourteen,  and  forty -eight  hours,  and  then  transferred 
to  75%  alcohol.    (2)  Picric=sublimate=osmic  acid  solution.     A  mix- 
ture of  ioo  c.c.   of  a  cold  saturated  aqueous  picric  acid  solution  with 
100  c.c.  of  saturated  sublimate  solution  is  made,  into  which  is  poured 
20  c.c.  of  a  2%  osmic  acid  solution.      2  c.c.  of  glacial  acetic  acid  may 
also  be  added.     Tissues  fixed  by  either  of  these  fluids  may  be   treated 
with  pyroligneous  acid  or  tannin.     The  crystals  of  sublimate  must  be 
removed  by  iodized  alcohol. 

25.  Nitric  Acid. — Small  objects  may  be  fixed  in  about  six  hours  in 
3%  to  5%  nitric  acid  (sp.  gr.  1.4).     A  longer  immersion  is  injurious, 
as  certain  nuclear  structures  are  affected.     After  washing  thoroughly  in 
running  water,  the  tissues  are  treated  as  usual  with  alcohols  of  increasing 
concentration. 

26.  Chromic   acid    is  used   in   a    ^3%   to  i%    aqueous   solution. 
Small  pieces  are  fixed  for  twenty-four  hours,  larger  ones  for  a  longer  time, 
even  weeks.     The  quantity  of  the  fixing  fluid  should  be  at  least  more 
than  fifty  times  the  volume  of  the  tissues  to  be  fixed.     The  objects  are 
subsequently  washed  in  running  water  and  run  through    the  ascending 
alcohols.     This  last  should  be  done  in  the  dark. 

Two  or  3  drops  of  formic  acid  may  be  advantageously  added  to 
each  ioo  c.c.  of  chromic  acid  solution  (C.  Rabl,  85). 

27.  Miiller's  Fluid.— 

Potassium  bichromate 2  to  2.5  gm. 

Sodium  sulphate i        " 

Water loo     c.c. 

With  this  solution  it  requires  several  weeks  for  proper  fixation,  and  the 
process  must  be  conducted  in  the  dark.  During  the  first  few  weeks  the 
solution  should  be  changed  every  few  days,  and  later  once  a  week. 


INFILTRATION    AND    IMBEDDING.  25 

According  to  the  results  desired,  the  pieces  are  either  washed  out  in  run- 
ning water  and  subsequently  treated  in  the  usual  manner  with  alcohol,  or 
they  are  placed  directly  in  70%,  which  is  later  replaced  by  80  %  and 
90%  alcohol.  It  is  important  that  all  these  procedures  should  take  place 
in  the  dark. 

28.  Zenker's  Fluid.— 

Potassium  bichromate 2.5  gm. 

Sodium  sulphate I  " 

Corrosive  sublimate 5  " 

Glacial  acetic  acid 5  c-c- 

Water 100  " 

It  is  advisable  to  add  the  glacial  acetic  acid  in  proper  proportion  to 
the  quantity  of  the  solution  to  be  used,  and  not  to  add  it  to  the  stock  solution. 
The  tissues  are  allowed  to  remain  for  from  six  to  twenty-four  hours  in  this 
mixture,  in  which  they  float  for  a  short  time.  They  are  then  washed  in 
running  water  for  from  twelve  to  twenty-four  hours,  and  transferred  to 
gradually  concentrated  alcohols.  Crystals  of  sublimate  which  may  be 
present  are  removed  with  iodized  alcohol.  Zenker's  fluid  penetrates 
easily,  and  fixes  nuclear  and  protoplasmic  structures  equally  well  without 
decreasing  the  staining  qualities  of  the  elements. 

29.  The  use  of  Erlicki's  fluid  (potassium  bichromate,   2^  gm.; 
cupric  sulphate,  0.5  gm.,  and  water,  100  c.c.)  is  quite  similar  to  that 
of  Miiller's,  except  that  it  acts  much  more  quickly.     A  temperature  of 
30°  C.  to  40°  C.  shortens  the  process  in  both  cases  considerably,  Miiller's 
fluid  fixing  in  eight  and  Erlicki's  in  three  days. 

30.  Formalin  (Formol). — Of  recent  years  formalin,  which    is   a 
40  %  solution  of  the  gas  formaldehyd  in  water,  has  been  much  used  as  a 
fixing  fluid.      It  is  best  employed  in  the  form  of  a  solution  made  by  add- 
ing 10  parts  of  formalin  to  90  parts  of  water  or  normal  saline  solution. 
Small  pieces  of  tissue  remain  in  this  solution  for  from  twelve  to  twenty- 
four  hours,  larger  pieces  or  organs  a  number  of  days  or  weeks,  and  are 
then  transferred  to  90%  alcohol. 

We  have  attempted  to  give  only  the  fixing  and  hardening  fluids  com- 
monly employed  for  general  purposes.  There  are  numerous  other  fluids 
used  for  special  purposes  ;  these  will  be  noticed  under  the  headings  of  the 
corresponding  tissues  and  organs. 


B.  INFILTRATION  AND  IMBEDDING. 

31.  To  obtain  sections  from  objects  already  fixed,  it  is  above  all 
necessary  that  they  should  have  a  certain  consistency,  which  they  obtain 
in  90%  alcohol.  It  is  not  advisable  to  attempt  the  free-hand  sectioning 
of  objects  that  have  not  previously  been  especially  prepared  for  this  treat- 
ment, as  crumbling  of  the  sections  and  falling  apart  of  the  loosely  con- 
nected tissues  are  the  results.  To  avoid  this,  infiltration  masses  are  used. 
The  tissue  is  placed  in  a  fluid  medium  which  penetrates  it  throughout  and 
then  hardens  into  a  solid  mass  on  cooling  or  on  the  evaporation  of  the 
solvent.  The  object  thus  infiltrated  and  imbedded  can  then  be  cut,  the 
natural  position  of  its  different  elements  being  preserved  in  the  section. 

The  commonest  infiltration  masses  are  paraffin  and  celloidin  (collo- 
dion or  photoxylin). 


26  THE    MICRCOSOPIC    PREPARATION. 


J.    PARAFFIN. 

32.  In  describing  the  method  of  paraffin  infiltration  and  imbedding  it 
is  assumed  that  the  tissues  have  been  previously  fixed  and  hardened  and  are 
in  alcohol  ready  for  further  manipulation.  From  the  hardened  tissues 
small  flat  pieces  are  cut  with  a  sharp  knife  or  razor.  If  possible,  they 
should  be  square,  rectangular,  or  triangular  in  shape,  their  surfaces  not 
exceeding  ^  square  inch,  and  their  thickness  from  ^  to  ^  of  an  inch. 
Pieces  of  larger  size  may  be  imbedded,  if  desired,  provided  the  requisite 
care  be  exercised.  The  pieces  selected  are  placed  in  absolute  alcohol,  in 
which  they  remain  until  thoroughly  dehydrated.  From  the  latter  they 
can  not  be  passed  directly  into  paraffin,  as  alcohol  is  not  a  solvent 
of  that  substance,  and,  consequently,  the  preparation  would  not  be  infil- 
trated with  the  imbedding  mass.  The  pieces  of  tissue  are  therefore 
first  placed  in  some  fluid  which  mixes  with  absolute  alcohol  and  at  the 
same  time  dissolves  the  paraffin.  There  are  many  such  reagents,  as  xylol, 
toluol,  chloroform,  and  a  number  of  oils  (oil  of  turpentine,  oil  of  cedar, 
oil  of  origanum,  etc.).  Of  these  reagents  xylol  may  be  recommended 
for  general  use.  In  the  xylol  the  tissues  remain  for  from  two  to  twelve 
hours,  the  time  depending  somewhat  on  the  size  of  the  pieces  and  on  the 
density  of  the  tissue.  When  thoroughly  permeated  by  the  xylol,  they  are 
transparent.  From  the  xylol  (toluol,  chloroform,  or  oils)  the  tissues  are 
placed  in  melted  paraffin.  Two  kinds  of  paraffin  are  used,  one  having  a 
melting  point  of  38°  to  40°  C. — soft  paraffin — and  another  with  a  melt- 
ing point  of  50°  to  58°  C. — so-called  hard  paraffin.  The  paraffin  should 
always  be  filtered  before  using.  It  is  essential  that  melted  paraffin  have  a 
constant  temperature  while  the  tissues  are  being  infiltrated.  This  is 
attained  by  placing  the  receptacle  containing  the  paraffin  in  a  paraffin 
oven  regulated  by  means  of  a  thermostat  to  a  temperature  about  two 
degrees  above  the  melting  point  of  the  hard  paraffin. 

Filtered  hard  and  soft  paraffin  may  be  kept  in  suitable  glass  beakers 
in  respective  compartments  in  the  paraffin  oven.  After  the  tissues  are 

thoroughly  permeated  with  the  xylol, 
this  is  poured  off  and  melted  soft 
paraffin  added,  and  the  dish  replaced 
in  the  paraffin  oven.  In  the  soft 
paraffin  the  tissues  remain  from  one  to 
four  hours,  at  the  end  of  which  time 
the  soft  paraffin  is  poured  off  and 
hard  paraffin  added,  and  the  dish 
again  placed  in  the  oven.  In  the 
hard  paraffin  the  tissues  remain  from 

Fig.  2. — Box  for  imbedding  tissues.  ,        ,  j  , .  , 

two  to  twelve  hours,  depending  on  the 
size  of  the  pieces.  They  are  now 

ready  to  be  imbedded.  Two  metallic  L's  are  placed  together  on  a 
glass  or  metal  plate  in  such  a  way  as  to  make  a  rectangular  box. 
(Fig.  2.)  This  is  filled  with  melted  hard  paraffin  taken  from  the 
oven.  Before  the  paraffin  cools,  the  piece  of  tissue  to  be  imbedded 
is  taken  from  the  hard  paraffin  in  the  oven  and  placed  with  one 
of  its  flat  surfaces  against  one  end  of  the  box.  If  several  pieces  of 
tissue  are  to  be  imbedded,  a  piece  may  thus  be  placed  in  each  end  of 
the  box.  While  transferring  the  tissues  from  the  hard  paraffin  to  the 
imbedding  box  they  should  be  handled  with  forceps,  the  blades  of 


INFILTRATION    AND    IMBEDDING.  2/ 

which  have  been  warmed  in  a  flame.  As  soon  as  the  paraffin  in  which 
the  tissues  are  imbedded  has  cooled  sufficiently  to  allow  the  formation  of 
a  film  over  the  melted  paraffin,  the  imbedding  box  is  placed  in  a  dish  of 
cold  water.  This  cools  the  paraffin  quickly  and  prevents  its  becoming 
brittle.  A  stay  of  from  five  to  ten  minutes  in  the  cold  water  hardens  the 
paraffin  so  that  the  L's  may  be  removed,  and  the  paraffin  block  containing 
the  imbedded  tissue  may  be  taken  from  the  plate.  It  is  well  to  place  the 
paraffin  block  thus  obtained  back  into  the  cold  water  for  a  short  time,  so 
that  it  may  become  hard  all  the  way  through.  As  the  paraffin  often 
adheres  closely  to  the  glass  or  metal  plate  and  the  L's,  it  is  advisable  to 
cover  these  parts  with  a  very  thin  layer  of  glycerin  before  imbedding. 
There  is  then  no  difficulty  in  separating  them  from  the  paraffin  block. 

33.  If  a  large  number  of  small  pieces  of  tissue  are  to  be  imbedded, 
it  is  often  advantageous  to  carry  on  their  infiltration  with  hard  paraffin  in 
a  flat  dish  of  suitable  size.     This  may  then  be  taken  from  the  paraffin  oven 
after  thorough  infiltration  has  been  attained  and  the  several  pieces  of  tissue 
arranged  on  the  bottom  of  the  dish.     As  soon  as  a  film  forms  over  the 
paraffin  the  dish  is  placed  carefully  in  cold  water  and  the  paraffin  allowed 
to  harden.      The  large  piece  of  paraffin  thus  obtained  may  then  be  cut 
into  several  smaller  pieces,  each  containing  a  piece  of  the  imbedded  tissue. 
The  dish  used  for  this  purpose  should  be  coated  on  the  inside  with  a 
thin  layer  of  glycerin. 

34.  On  transferring  an  object  from  one  fluid  into  another,  so-called 
currents  of  diffusion  occur,  which  produce,  especially  in  such  tissues  as 
contain  cavities,  shrinkage  and  tearing.     This  often  results  in  totally 
changing  the  finer  structure  of  the  tissues.     It  is  therefore  necessary  to 
proceed  w;th  greater  caution  than  in  the  method  above  indicated. 

Mixtures  containing  different  percentages  of  alcohol  and  the  inter- 
mediate fluid  (xylol,  toluol,  chloroform)  may  be  prepared,  and  the  object, 
according  to  its  delicacy,  passed  through  a  greater  or  smaller  number  of 
such  solutions.  In  ordinary  cases  a  single  mixture  of  alcohol  and  the  in- 
termediate fluid  is  sufficient,  the  object  remaining  in  the  solution  for  a 
length  of  time  varying  with  its  size  before  being  passed  into  the  pure  in- 
termediate fluid.  This  part  of  the  treatment  may  of  course  be  slowed  or 
hastened  according  to  the  number  of  such  mixtures,  each  succeeding  one 
containing  more  and  more  of  the  intermediate  fluid. 

35.  After  the  object  has  been  passed  into  the  pure  intermediate  fluid 
it  should  be  just  as  carefully  passed  into  the  infiltrating  fluid.   If  paraffin  is 
to  be  used  and  the  object  be  delicate,  the  following  method  is  advisable  : 
The  object  is  placed  in  a  glass  vessel  half  filled  with  the  intermediate  fluid, 
into  which  a  few  pieces  of  soft  paraffin  are  dropped.     The  vessel  is  then 
covered  and  allowed  to  remain  at  the  temperature  of  the  room.     When  the 
paraffin  is  dissolved  the  cover  is  removed  and  the  vessel  placed  in  a  par- 
affin oven  kept  at  a  temperature  corresponding  to  the  melting  point  of  the 
paraffin.     The  volatile  intermediate  fluid  evaporates  gradually,  and  in  a 
few  hours  the  object  is  infiltrated  with  an  almost  pure  soft  paraffin.     It  may 
now  be  transferred  into  pure  melted  hard  paraffin.     In  this  the  tissue 
remains  for  a  longer  or  shorter  time,  according  to  its  size. 

36.  High   temperatures   are,  as   a   rule,  injurious   to  tissues.     This 
should  always  be  borne  in  mind,  and  the  student  should  aim  to  keep  his 
specimens  at  the  lowest  possible  temperature  conducive  to  proper  infiltra- 
tion.    If  for  any  reason  higher  temperatures  become  necessary,  the  ex* 


28 


THE    MICROSCOPIC    PREPARATION. 


posure  of  the  tissues  to  their  action  should  be  as  brief  as  possible.  The 
paraffins  most  used  have  a  melting  point  of  40°  to  60°  C.  The  kind  of 
paraffin  used  should  depend  upon  the  temperature  of  the  room  in  which 
the  sectioning  is  to  be  done.  It  is  even  well  to  have  different  mixtures  of 
hard  and  soft  paraffins  at  hand,  so  that,  if  the  temperature  of  the  room 
be  low,  tissues  may  be  imbedded  in  a  softer  mixture,  and  vice  versa. 

37.  The  process  of  infiltrating  and  imbedding  in  paraffin  is  repre- 
sented by  the  following  diagram  (instead  of  xylol,  other  intermediate 
fluids  may  be  used)  : 


I 


Alcohol, 

t 
Abs.  alcohol   - 

t 
Alcohol  -xylol  mixture 

t 
—Xylol  -*•— 

t 
Xylol-paraffin  (cold) 

t 
Xylol-paraffin  (in  paraffin  oven) 


Soft   paraffin  -^ 


Hard  paraffin 

f 
Imbedding 

38.  The  size  and  density  of  the  tissues  must  necessarily  regulate  the 
length  of  time  necessary  for  their  proper  infiltration.  It  is  therefore  hardly 
possible  to  give  any  definite  figures.  In  presenting  the  following  table  we 
have  taken  as  a  standard  any  tissue  that  has  the  general  consistency  of 
liver  fixed  in  alcohol.  The  time  is  given  in  hours,  and  should  in  each 
case  be  regarded  as  a  minimum.  A  longer  stay  in  any  one  fluid  will, 
under  favorable  circumstances,  do  no  harm. 


SMALL  OB- 
JECTS UNDER 
I  MM.  IN 

DIAMETER. 

MIDDLE-SIZED 
OBJECTS  UP 
TO  5  MM.  IN 
DIAMETER. 

LARGE  OB- 
JECTS UP  TO  10 
MM.  IN 

DIAMETER. 

VERY  LARGE  OB- 
JECTS,   ALTHOUGH 
NOT  MORE  THAN  A 
FEW  CM.  IN  DI- 
AMETER. 

Absolute  alcohol    .    .    . 

2 

6 

24 

For   a    longer    or 

Xylol  

# 

3 

6 

shorter   time    in 

the    fluids,     ac- 

From  now  on  in    par- 
affin oven  : 

cording    to    the 
size  of  the  object. 

Soft  paraffin    

y* 

3 

6 

Hard  paraffin      .... 

i 

3 

6 

2.  CELLOIDIN. 

The  best  and  most  convenient  celloidin  to  use  in  microscopic  work  is 
Schering's  granular  celloidin,  put  up  in  i -ounce  bottles.  Of  this  a 
stock  or  thick  solution  is  prepared  by  dissolving  6  gm.  of  the  celloidin  in 
100  c.c.  of  equal  parts  of  absolute  alcohol  and  ether.  Of  this,  when 
required,  a  thin  solution  is  prepared  by  diluting  a  quantity  of  the  stock 
solution  with  an  equal  quantity  of  the  ether  and  alcohol  solution. 


INFILTRATION    AND    IMBEDDING.  2Q 

39.  The  hardened  tissues  are  cut  into  small  pieces,  which  should  not 
be  much  more  than  ^  of  an  inch  in  thickness  and  not  have  a  surface 
area  of  more  than  ^  of  a  square  inch.      Much  larger  pieces  of  tissue 
may  be  imbedded  in  celloidin.     This  is  not  advised,  however,  unless  it  is 
necessary  to  show  the  whole  of  the  structure  to  be  studied.     The  pieces 
to  be  imbedded  are  placed  for  twenty-four  hours  in  absolute  alcohol,  and  are 
then  transferred  for  twenty-four  hours  to  a  mixture  of  equal  parts  of  abso- 
ute  alcohol  and  ether.    Then  they  go  into  the  thin  celloidin  solution,  where 
they  remain  for  from  twenty-four  hours  to  several  days,  depending  on  the 
size  and  density  of  the  pieces  to  be  imbedded.     The  pieces  of  tissue  are 
then  transferred  to  the  thick  celloidin  solution,  where  they  again  remain 
for  from  twenty-four  hours  to  several  days.     If  it  is  desired  to  imbed  large 
pieces,  especially  if  these  be  of  the  medulla  or  brain,  the  stay  in  the  cel- 
loidin solutions  should  be  lengthened  to  several  weeks.     The  hardening 
of  the  celloidin  may  now  be  obtained  by  one  of  several  methods. 

40.  A  sufficient  quantity  of  the  stock  or  thick  celloidin  solution  to 
cover  well  the  tissues  to  be  imbedded  is  poured  into  a  flat  dish  large 
enough  to  allow  the  pieces  to  be  imbedded  to  be  arranged  on  its  bottom 
and  leave  a  space  of  about  ^  of  an  inch  between  adjacent  pieces.     The 
dish  is  then  covered,  not  too  tightly,  and  set  aside  to  allow  the  ether  and 
alcohol  to  evaporate.     In  one  or  two  days  the  celloidin  is  usually  hard 
enough  to  cut  into  small  blocks,  each  block  containing  a  piece  of  the 
imbedded  tissue.     The  blocks  of  celloidin  are  now  further  hardened  by 
placing  them  in  80%  alcohol.     A  stay  of  several  hours  in  this  alcohol  is 
usually  sufficient  to  give  them  the  hardness  required  for  section  cutting. 
After  the  celloidin  pieces  have  obtained  the  right  degree  of  hardness  they 
are  to  be  stuck  to  small  pieces  of  pine  wood  or  vulcanized  fiber  so  that  they 
may  be  clamped  into  the  microtome.    This  is  done  in  the  following  way  : 
A  piece  of  celloidin  containing  a  piece  of  tissue  is  trimmed  with  a  sharp 
knife  so  that  only  a  rim  of  celloidin  about  ^  °f  an  incn  ^n  thickness 
surrounds  the  piece  of  tissue.      It  is  now  placed  for  a  few  moments  in  the 
ether  and  alcohol  solution.     This  is  to  soften  the  surfaces  of  the  celloidin. 
One  end  of  a  small  pine-wood  or  vulcanized-fiber  block  about  one  inch  long, 
the  cut  end  of  which  has  a  surface  area  slightly  larger  than  the  celloidin 
block,  is  dipped  for  a  few  moments  into  the  ether  and  alcohol  solution  and 
then  into  the  thick  celloidin.     The  celloidin  block  is  now  taken  from  the 
ether  and  alcohol  solution,  dipped  into  the  celloidin,  and  pressed  against 
the  end  of  the  wooden  or  vulcanized-fiber  block,  which  has  been  coated 
with  the  celloidin.     The  whole  is  now  set  aside  for  a  little  while  to  allow 
the  celloidin  to  harden  slightly,  and  is  then  placed  in  80%  alcohol.     In 
the  alcohol  it  may  remain  indefinitely ;   it  may,   however,  be  used  for 
cutting  as  soon  as  it  again  becomes  hard. 

41.  The  piece  of  tissue  to  be  imbedded  may  be  mounted  at  once  on 
pine-wood  or  vulcanized-fiber  blocks  from  the  thick  celloidin  solution  by 
pouring  a  small  amount  of  thick  celloidin  over  one  end  of  the  block  and 
placing  the  piece  of  tissue  from  the  thick  celloidin  solution  onto  the  layer 
of  celloidin  on  the  block.      In  three  to  four  minutes  a  layer  of  the  thick 
celloidin  solution  is  poured  over  the  piece  of  tissue  and  the  end  of  the 
block.      It  may  be  necessary  to  do  this  several  times  if  the  piece  of  tissue 
is  large  or  of  irregular  shape.     The  block  is  now  set  aside  for  about  five 
minutes,  and  is  then  placed  in  80%  alcohol,  where  it  remains  until  the 
celloidin  is  hard,  or  until  it  is  desired  to  cut  sections. 


30  THE    MICROSCOPIC    PREPARATION. 

42.  The  tissues  may  be  imbedded  by  pouring  the  thick  celloidin,  to- 
gether with  the  objects,  into  a  small  box  made  of  paper.    The  surface  of  the 
celloidin  hardens  in  about  an  hour  (preliminary  hardening),  after  which 
the  whole  is  transferred  to  80  %   alcohol,  in  which  the  final  hardening 
takes  place.     The  paper  is  then  removed,  the  block'of  celloidin  trimmed 
to  a  convenient  size  and  fastened  on  a  block. 

While  being  cut,  celloidin  preparations  are  kept  moistened  with  80  % 
alcohol.  Organs  consisting  of  tissues  of  varying  consistency,  as  well 
as  very  dense  objects,  can  be  cut  with  better  results  in  celloidin  than  in 
paraffin.  On  the  other  hand,  celloidin  sections  can  never  be  cut  as  thin 
as  parafrin  sections,  and  the  after-treatment  (see  below),  fixation  on  the 
slide,  etc.,  are  much  more  complicated  than  in  the  case  of  paraffin  sec- 
tions. 

43.  The  following  is  a  diagram  showing  the  process  of  infiltration 
and  imbedding  in  celloidin. 


alcohol 

t 
Abs.  alcohol 

t 

Abs.  alcohol  and  ether  (in  equal  parts) 
t 

Thin  celloidin  solution 

f. 
Thick  celloidin  solution 

t 
Imbedding 

t 
80%   alcohol 

3.  CELLOIDIN-PARAFFIN. 

44.  To  combine  the  advantages  which  infiltration  in  celloidin  and  in 
paraffin  offer,  a  method  of  celloidin  -paraffin  infiltration  is  recommended. 
Preparations  that  have  been  imbedded  in  celloidin  and  hardened  in  80% 
alcohol  are  placed  for  about  twelve  hours  in  90%  alcohol,  from  which 
they  are  transferred  to  a  mixture  of  equal  parts  of  oil  of  origanum  and 
90%  alcohol.  They  are  then  immersed  for  a  short  time  in  pure  origa- 
num oil,  then  in  a  mixture  of  equal  parts  of  origanum  oil  and  xylol,  and 
finally  in  pure  xylol.  From  this  point  the  regular  method  of  infiltrating 
with  paraffin  is  followed,  care  being  taken  that  the  pieces  remain  for  as 
short  a  time  as  possible  in  the  different  fluids,  in  order  that  the  celloidin 
may  not  become  brittle. 

Very  thin  sections  may  be  obtained  by  painting  the  cut  surface  with 
a  thin  layer  of  a  very  dilute  celloidin  solution.  This  hardens  and  gives 
the  tissue  a  greater  consistency.  This  treatment  is  useful  in  the  combined 
celloidin  -paraffin  method,  as  well  as  when  paraffin  alone  is  used. 


C.  THE  MICROTOME  AND  SECTIONING. 

Instruments  known  as  microtomes  have  been  devised  in  order  that 
section  cutting  may  be  rendered  as  independent  as  possible  of  the  skill 
of  the  individual,  but  more  especially  to  obtain  series  of  sections  of  uni- 
form thickness.  Their  construction  varies  greatly.  Some  of  these  in- 


THE    MICROTOME    AND    SECTIONING.  3! 

struments,  as  the  so-called  rocking  microtomes,  are  so  specialized  that  they 
only  cut  paraffin  objects  when  the  knife  is  transversely  placed.  Others 
have  a  more  general  function,  celloidin  as  well  as  paraffin  objects  being 
sectioned  with  the  knife  in  any  position.  To  the  latter  class  belong  the 
sliding  microtomes.  Of  these,  two  types  are  in  general  use  in  this 
country,  and  may  therefore  be  more  thoroughly  discussed. 

45.  In  figure  3  is  shown  an  instrument  which  may  be  recommended 
for  general  laboratory  work.  This  instrument  consists  of  a  horizontal 
base  which  rests  on  the  table,  and  a  vertical  plate  (#),  and  a  slide  (£)  which 
supports  a  block  (V),  to  which  is  fastened  a  knife  by  means  of  a  thumb- 
screw (V).  On  the  other  side  of  the  vertical  plate  is  a  metal  frame  (*), 
into  which  are  fastened  the  paraffin  and  celloidin  blocks ;  this  frame  is 
attached  to  a  slide  (/),  which  may  be  elevated  or  lowered  by  a  feed  (£"). 
This  feed  consists  of  a  micrometer  screw  acting  on  the  lower  surface 
of  the  slide.  The  micrometer  screw  is  provided  with  a  milled  head, 
divided  into  a  definite  number  of  parts  which  bear  a  definite  rela- 


Fig.  3. — Laboratory  microtome. 

tion  to  the  pitch  of  the  micrometer  screw.  The  instrument  shown 
in  the  figure  is  further  provided  with  a  lever  (/«),  which  may  be 
so  adjusted  as  to  move  the  milled  head  on  the  micrometer  screw 
i  or  any  given  number  of  notches  at  each  movement  of  the  lever; 
and  as  each  notch  on  the  milled  head  has  a  value  of  5  microns 
(•-^-Q-  of  an  inch),  every  time  the  milled  head  is  moved  i  notch 
(toward  the  manipulator)  the  slide  carrying  the  clamp  holding  the  tissue 
is  elevated  5  microns;  2  notches  would  elevate  the  tissue  10  microns 
(•yg^-g-  of  an  inch)  ;  4  notches,  20  microns  (y^Vff  °^  an  incn)>  etc-  ^ 
is  not  essential  to  have  a  lever  attached  to  the  instrument  as  above 
described,  although  this  is  very  convenient ;  if  not  present,  the  milled 
head  is  moved  the  desired  number  of  notches  with  the  hand. 

46.  In  cutting  paraffin  sections  with  the  sliding  microtome  the 
knife  is  placed  at  an  angle  of  about  35°  to  40°  to  the  horizontal  plate  of 
the  microtome.  Sections  are  cut  more  easily  with  the  knife  in  this  posi- 


32  THE    MICROSCOPIC    PREPARATION. 

tion  than  when  the  knife  is  placed  at  right  angles  to  the  microtome,  as  is 
often  recommended,  and  it  does  not  seem  that  the  tissues  suffer  materially 
from  distortion  when  they  are  cut  with  the  knife  at  an  angle,  as  is  some- 
times claimed. 

Before  fastening  the  paraffin  blocks  into  the  clamp  on  the  microtome, 
preparatory  to  cutting  sections,  the  paraffin  is  trimmed  with  a  sharp  knife 
from  the  end  of  the  paraffin  block  until  the  tissue  is  nearly  exposed,  care 
being  taken,  however,  to  leave  a  flat  surface.  The  top  of  the  paraffin 
block  is  then  beveled  off  on  three  sides  to  within  a  very  short  distance 
of  the  tissue.  The  fourth  side,  that  which  faces  the  knife  when  the  block 
is  clamped  in  the  microtome,  should  be  trimmed  only  to  within  about  ^  of 
an  inch  of  the  tissue.  This  edge  of  paraffin  is  made  use  of,  as  will  be  seen 
in  a  moment,  for  preventing  the  sections  from  curling  while  they  are  being 
cut.  The  paraffin  block  is  now  ready  to  be  clamped  in  the  microtome. 
This  is  done  in  such  a  way  that  the  paraffin  block  just  escapes  the  knife 
when  drawn  over  it.  A  number  of  rather  thick  sections  (20  to  40 
microns)  are  cut  by  moving  the  micrometer  screw  from  right  to  left  4 
to  8  notches  every  time  the  knife  has  been  drawn  over  the  paraffin 
block  and  has  been  brought  back  again,  until  it  is  noticed  that  the  knife 
touches  all  parts  of  the  top  of  the  paraffin  block,  or  until  the  tissue  is 
fairly  exposed.  The  succeeding  sections  may  now  be  kept.  It  may  per- 
haps be  well  to  state  that  it  is  better  not  to  try  to  cut  very  thin  sections 
at  the  beginning ;  sections  20  to  15  microns  in  thickness  will  answer  very 
well.  To  begin  with,  then,  the  milled  head  of  the  micrometer  screw  is 
turned  4  notches  from  left  to  right,  and  the  knife  is  drawn  over  the  block 
with  a  steady,  even  pull,  and  without  using  undue  pressure.  Usually  the 
sections  will  curl  up  as  they  are  being  severed  from  the  paraffin  block. 
This  may  very  readily  be  prevented  by  holding  the  tip  of  a  camel' s-hair 
brush,  which  has  been  pointed  by  drawing  it  between  the  lips,  against  the 
edge  of  the  section  as  soon  as  it  begins  to  curl.  A  little  practice  will 
enable  one  to  do  this  almost  automatically.  The  sections  are  transferred 
to  paper  by  means  of  the  camel's-hair  brush,  which  process  is  facilitated 
if  the  brush  has  been  slightly  moistened  with  saliva,  as  the  section  will 
then  adhere  lightly  to  the  brush. 

47.  If -the  tissues  are  well  imbedded  and  not  too  hard,  and  if  the  knife 
is  sharp  and  properly  adjusted,  paraffin  sections  may  be  cut  in  such  a  way 
that  each  succeeding  section  adheres  to  the  preceding  one,  so  that  actual 
ribbons  of  paraffin  sections  may  be  made.  In  order  to  do  this,  the  knife 
should  be  at  right  angles  to  the  microtome.  The  paraffin  block  should  be 
trimmed  in  such  a  way  that  when  clamped  in  the  microtome  ready  for 
cutting  sections,  the  surface  of  the  paraffin  block  facing  the  knife  should 
be  exactly  parallel  to  its  edge,  also  to  the  opposite  side  of  the  block.  In 
other  words,  2  sides  of  the  paraffin  block  should  be  parallel  to  each 
other  and  to  the  knife  ;  then  if  the  paraffin  is  of  the  right  consistency, 
which  must  be  ascertained  by  trying,  the  sections  as  they  are  cut  will  ad- 
here to  each  other  and  form  a  ribbon.  If  the  sections  do  not  adhere  to 
each  other  it  is  quite  probable  that  the  paraffin  is  a  little  too  hard.  This 
may  often  be  remedied  by  holding  an  old  knife  or  other  metallic  instru- 
ment which  has  been  heated  in  a  flame  near  the  two  parallel  surfaces  for  a 
few  moments.  Care  should  be  taken  not  to  allow  this  instrument  to  touch 
the  paraffin.  This  is  a  very  convenient  and  rapid  way  of  cutting  par- 
affin sections.  To  facilitate  the  cutting  of  a  paraffin  possessing  a  rela- 


THE    MICROTOME   AND    SECTIONING.  33 

tively  low  melting  point  in  a  room  with  a  high  temperature,  the  cooled 
knife  of  Stoss  may  be  used.  This  is  so  made  that  a  stream  of  ice-water 
may  be  passed  through  a  tube  running  through  the  entire  length  of  the 
back  of  the  blade. 

48.  Celloidin  Sections. — Before  fastening  the  block  of  wood  or  vul- 
canized fiber  to  which  the  celloidin  blocks  have  been  fixed  in  the  clamp 
on  the  microtome,  the  celloidin  should  be  trimmed  with  a  sharp  knife 
from  the  top  of  the  block  until  the  tissue  is  nearly  exposed,  care  being 
taken  to  leave  a  flat  surface.  The  sides  of  the  celloidin  block  are  then 
trimmed  down,  if  necessary,  to  within  about  y1^-  of  an  inch  of  the  tissue. 
The  block  is  now  clamped  in  the  microtome  at  such  a  level  that  it  just 
escapes  the  knife  when  drawn  over  it.  The  knife  is  placed  at  an  angle  of 
about  45°,  or  at  even  a  greater  angle.  During  the  process  of  cutting,  the 
knife,  as  also  the  tissue,  must  be  kept  constantly  moistened  with  80% 
alcohol.  This  is  perhaps  most  easily  accomplished  by  taking  up  the  80% 
alcohol  with  a  rather  large  camel' s-hair  brush  and  dipping  this  on  the 


Fig.  4. — Sliding  microtome  of  Jung.  Medium-sized  model  No.  IV. 
The  instrument  is  shown  from  the  left.  On  the  right  side  is  the  plate  placed  at  an 
acute  angle,  as  a  carrier  for  the  sliding  block  to  which  the  knife  is  fastened.  Both  are 
partly  visible.  The  screws  c  serve  to  fix  the  knife  (absent  in  the  figure)  in  place.  The 
rod  (J)  serves  to  turn  the  screws.  On  the  left  side  of  the  microtome  is  fastened  the 
diagonally  placed  side  plate.  On  this,  behind,  rests  (in  the  figure  to  the  right)  the  microm- 
eter screw,  and  in  front  (in  the  figure  to  the  left)  the  object  carrier. 


celloidin  block  and  on  the  knife.  A  number  of  rather  thick  sections  are 
cut  until  the  knife  touches  the  entire  surface  of  the  block  or  until  the  tis- 
sue is  well  exposed.  The  sections  may  now  be  kept.  The  block  is  raised 
20  to  15  microns,  and  the  knife,  which  should  be  well  moistened  with 
80%  alcohol,  is  drawn  over  the  block  with  a  steady  pull,  not  with  a 
jerk.  The  sections  are  transferred  from  the  knife  to  distilled  water. 
This  is  perhaps  most  conveniently  done  by  placing  the  ball  of  one  of  the 
fingers  of  the  left  hand  under  the  edge  of  the  knife,  in  front  of  the  sec- 
tion, and  drawing  the  section  down  onto  the  finger  with  the  camel' s-hair 
brush.  The  finger  is  then  dipped  into  the  distilled  water  when  the  sec- 
3 


34  THE    MICROSCOPIC    PREPARATION. 

tion  floats  off.  If  the  sections  can  not  be  stained  within  a  few  hours  after 
they  are  cut,  they  are  best  transferred  to  a  dish  containing  80  %  alcohol, 
in  which  they  may  be  left  until  it  is  desired  to  stain  them. 

49.  The  other  type  of  sliding  microtome  to  be  specially  mentioned  is 
that  suggested  by  Professor  Thoma  and  made  by  R.  Jung,  of  Heidelberg. 
(Fig.  4.)  The  immovable  portions  of  this  microtome  consist  of  four 
plates,  of  which  the  lower  rests  as  a  horizontal  base  on  a  table.  A  second 
vertically  placed  plate  rests  along  the  middle  of  this  base.  The  other  two 
are  fastened  one  on  each  side  of  the  second  plate  in  such  a  way  that  they 
are  directed  diagonally  outward  and  upward,  forming  with  the  vertical 
plate  acute  angles  whose  apices  are  directed  downward.  One  of  these  is 
attached  horizontally  to  the  vertical  plate,  the  other  obliquely,  one  end 
being  attached  lower  than  the  other,  thus  forming  an  incline. 

Into  the  angles  formed  by  the  side  and  vertical  plates  fit  solid  metal 
bodies,  which  can  be  easily  slid  backward  and  forward  on  the  smooth  sur- 
faces arranged  for  this  purpose.  On  these  metal  blocks  the  knife  and  the 
object  are  fastened,  and  they  are  therefore  called  the  knife-  and  object-car- 
riers. The  former  runs  on  the  horizontal,  the  latter  on  the  inclined  plane. 
The  several  holes  bored  in  the  upper  surface  of  the  knife-carrier  are  for 
the  screw  which  fastens  the  knife  in  whatever  position  is  most  convenient. 
The  knife  is  clamped  down  by  the  screw-head.  The  object-holder  con- 
sists of  an  arrangement  for  the  fixation  of  the  object.  This  may  be  a 
simple  clamp,  into  which  the  block  of  wood  is  fastened.  It  is,  however, 
often  necessary  to  move  the  object  to  be  cut  in  different  directions  to 
obtain  proper  orientation,  especially  in  the  sectioning  of  embryos.  In 
such  cases  an  object -carrier  provided  with  an  arrangement  for  orientation 
is  used.  In  the  carrier  is  fastened  a  rectangular  frame  of  metal  which,  by 
means  of  screws,  may  be  turned  on  two  axes  at  right  angles  to  each 
other  and  thus  fixed  in  any  given  position.  In  the  middle  of  this  revolv- 
ing frame  of  metal  is  an  aperture  into  which  a  cylinder  is  fitted.  In  the 
case  of  paraffin  preparations,  this  is  filled  with  paraffin  and  the  imbedded 
object  attached  to  its  upper  end  by  heating.  A  special  mechanism  is  pro- 
vided for  the  raising  and  lowering  of  the  cylinder.  The  newer  instru- 
ments are  made  on  the  same  principle  except  that  they  have  a  screw  at 
one  side  by  means  of  which  the  whole  apparatus  may  be  raised  or  lowered, 
an  arrangement  that  is  especially  adapted  for  long  objects.  Instead  of 
containing  a  cylinder,  the  clamp  may  be  made  to  fit  a  block  of  wood  ;  in 
this  case  the  object  is  melted  on  to  the  upper  surface  of  the  block. 

In  sectioning,  the  microtome  is  so  placed  before  the  operator  that  the 
plate  upon  which  the  knife-carrier  moves  is  to  the  right.  The  object -car- 
rier should  be  at  the  end  of  the  microtome  nearest  the  worker.  A  for- 
ward motion  of  this  carrier  on  its  ascending  path  will  cause  the  object  to 
be  raised.  As  the  knife-carrier  always  moves  in  a  horizontal  direction/ 
the  blade  will  cut  from  the  object  a  section  the  thickness  of  which 
will  correspond  to  the  distance  which  the  object  has  been  raised, 
and  this  is  regulated  by  the  distance  that  the  object -carrier  is  moved 
forward.  To  measure  this,  the  vertical  plate  of  the  microtome  and  the 
object-carrier  are  provided  with  a  scale  and  nonius  or  vernier.  To  obtain 
a  series  of  sections  of  exactly  equal  thickness,  the  arrangement  by  which 
the  object-carrier  is  moved  forward  by  hand  is  not  sufficiently  accurate. 
Very  exact  results  are  obtained  with  the  help  of  a  micrometer  screw, 
which  is  attached  behind  the  object-carrier  and  moves  the  object  a 
certain  distance  at  every  turn.  In  the  Thoma- Jung  microtome  a  single 


THE    MICROTOME    AND    SECTIONING.  35 

revolution  of  the  screw  raises  the  object  15/1*.  A  drum  attached  to  the 
screw  is  marked  off  at  its  periphery  into  fifteen  equal  parts ;  the  turning 
of  the  screw  one  degree,  therefore,  raises  the  object  i  p.  By  means 
of  a  cog  arrangement  it  is  possible  to  regulate  automatically  the  raising 
of  the  object  and  consequently  the  thickness  of  the  sections  in  the  series. 

Before  cutting,  the  paths  upon  which  the  knife-  and  object-carriers 
slide  must  be  carefully  cleaned  and  oiled  ;  so-called  machine  oil  (four 
parts  of  bone  oil  to  one  part  of  petroleum)  is  the  best  for  this  purpose. 
Enough  oil  should  be  used,  and  care  should  be  taken  that  the  knife-car- 
rier moves  easily  from  one  end  to  the  other  of  its  pathway.  The  micro- 
tome knife  should  now  be  fastened  into  its  holder,  and  the  blade  placed 
in  such  a  position  that  it  forms  an  acute  angle  with  the  upper  edge  of  the 
vertical  plate.  The  object  is  placed  on  the  object-carrier,  and  fixed  at 
the  desired  height,  with  the  micrometer  screw  resting  against  the  agate- 
plate  of  the  object-carrier.  The  knife-carrier  with  its  knife  is  now 
brought  toward  the  operator,  the  slightest  pressure  being  avoided,  as 
otherwise  the  layer  of  oil  disappears  and  the  sections  become  irregular  in 
thickness.  The  newest  Jung  microtomes  have  a  rod  pointing  downward 
on  the  side  of  the  knife-holder.  The  operator,  resting  a  finger  on  the 
anterior  surface  of  this  rod,  can  pull  the  knife  toward  him,  thus  avoiding 
the  possibility  of  any  pressure  on  the  apparatus. 

The  knife  having  brought  with  it  a  section,  it  is  often  seen  that  the 
latter  is  not  flat  on  the  blade,  but  rolled.  This  condition  may  be  avoided, 
as  has  been  stated,  by  holding  down  the  free  edge  of  the  section  with  a 
camel' s-hair  brush  held  in  the  left  hand.  There  are  also  so-called  section 
stretchers,  which  consist  of  rollers  of  different  diameters.  They  are  so 
attached  above  the  blade  of  the  knife  that  between  them  and  the  knife  is 
a  very  narrow  space  through  which  the  section  must  pass.  These  section 
stretchers  are  very  difficult  to  put  into  position,  and  their  action  is  uncer- 
tain, so  that  it  is  advisable  to  accustom  one's  self  to  the  brush  method, 
which  affords  good  results  after  a  little  practice. 

After  cutting  the  section  the  knife  is  pushed  back  to  the  opposite  end 
of  the  instrument  and  again  brought  forward  after  turning  the  micrometer 
screw,  thus  producing  a  second  section.  After  continued  section-cutting  the 
micrometer  screw  passes  through  its  attachment  to  its  full  length  and  must 
then  be  screwed  back  and  adjusted  anew  against  the  agate-plate.  During 
this  procedure  the  object -carrier  should  not  be  moved.  R.  Jung  has  re- 
cently produced  a  micrometer  screw  provided  with  a  reversible  arrange- 
ment by  which  the  tedious  process  of  turning  backward  is  avoided.  The 
knife  may  be  fastened  transversely  to  the  long  axis  of  the  microtome,  and 
if  the  paraffin  and  room  temperature  be  favorable,  ribbons  can  be  cut. 
Celloidin  sections  may  also  be  cut  with  this  instrument. 

50.  The  sliding  microtomes  may  be  provided  with  an  arrangement 
for  freezing  tissues — a  so-called  freezing  apparatus.  This  consists  of 
a  metal  plate  on  which  the  tissue  is  laid  ;  an  ether-atomizer  plays  upon  its 
lower  surface,  cooling  and  finally  freezing  the  object,  which  is  then  cut. 
A  drop  of  fluid  (physiologic  saline  solution,  water,  etc.)  is  placed  upon 
the  knife,  in  which  the  section  thaws  out  and  spreads.  A  better  and 
more  rapid  method  of  freezing  tissues  consists  in  the  use  of  compressed 
carbon  dioxid,  as  recommended  by  Mixter.  Cylinders  containing  about 
twenty  pounds  of  the  liquid  gas  may  be  obtained  from  Bausch  &  Lomb, 
who  also  make  a  small  microtome  designed  for  this  purpose.  In  figure  5 
is  shown  the  lower  third  of  a  cylinder  for  compressed  carbon  dioxid 


36  THE    MICROSCOPIC    PREPARATION. 

firmly  fastened  to  a  thick  board,  and  connected  by  means  of  a  short  piece 
of  strong  rubber  tubing  with  the  freezing  box  of  the  microtome.  The 
handle  of  the  escape  valve  is  from  8  to  10  inches  long,  so  that  -the 
quantity  of  escaping  gas  may  be  readily  controlled.  The  pieces  of  tis- 
sue are  placed  on  the  freezing  box  of  the  microtome  and  the  escape  valve 
slowly  opened  until  a  small  quantity  of  the  gas  escapes.  Small  pieces  of 
tissue  are  frozen  in  about  thirty  seconds  to  a  minute ;  tissues  taken  from 
alcohol  should  be  washed  for  a  short  time  in  running  water  before  freez- 
ing. A  strong  razor  may  be  used  for  cutting  sections ;  or  better,  a  well- 
sharpened  blade  of  a  carpenter's  plane,  as  suggested  by  Mallory  and 
Wright.  Sections  are  transferred  to  distilled  water  or  normal  salt  solu- 
tion, and  if  fixed  may  be  stained  at  once.  Sections  of  fresh  tissue 
should  be  taken  from  the  normal  salt  solution  and  transferred  to  a  fixing 
fluid. 

51.  It  is  impossible  to  cut  thin  sections  with  a  knife  that  is  not  sharp, 
or  with  one  that  is  nicked.  A  few  directions  as  to  sharpening  a  micro- 
tome knife  may  therefore  not  be  out  of  place.  For  this  purpose  a  good 


Fig.   5. — Apparatus  for  cutting  tissues  frozen  by  carbon  dioxide 

Belgian  hone  is  used,  which  should  be  moistened  or  lubricated  with  filtered 
kerosene  oil  as  necessity  demands.  While  sharpening  the  knife  it  is  grasped 
with  both  hands — with  one  by  the  handle,  with  the  other  by  the  end. 
The  hone  is  placed  on  a  table  with  one  end  directed  toward  the  person 
sharpening.  If  the  knife  is  very  dull,  it  is  ground  for  some  time  on  the 
concave  side  only  (all  microtome  knives  are  practically  plane  on  one  side 
and  concave  on  the  other),  with  the  knife  at  right  angles  to  the  stone. 
It  is  carried  from  one  end  of  the  stone  to  the  other,  edge  foremost,  giving 
it  at  the  same  time  a  diagonal  movement,  so  that  with  each  sweep  the 
entire  edge  is  touched  (see  Fig.  6).  In  drawing  back  the  knife,  the  edge 
is  slightly  raised.  The  knife  is  ground  on  the  concave  side  until  a  fine 
thread  (feather  edge)  appears  along  the  entire  edge.  It  is  then  ground 
on  both  sides,  care  being  taken  to  keep  the  knife  at  right  angles  to  the 
stone,  to  keep  it  flat,  and  to  use  practically  no  pressure.  It  is  a 
good  plan  to  turn  the  knife  on  its  back  when  the  end  of  the  stone  is 
reached.  On  the  return  stroke,  the  knife  is  again  held  at  right  angles 
to  the  stone,  the  same  diagonal  sweep  is  used  (see  Fig.  6),  so  that  the 


THE    MICROTOME    AND    SECTIONING.  37 

whole  edge  of  the  knife  is  touched  with  each  sweep.  The  grinding  on 
both  sides  is  continued  until  the  thread  above  mentioned  has  disappeared. 
The  knife  should  now  be  carefully  cleaned  and  stropped,  with  the  back  of 
the  knife  drawn  foremost.  The  strop  should  be  flat  and  rest  on  a  firm 
surface. 

Very  good  microtomes  are  manufactured  by  August  Becker  in  Gottin- 
gen.  Of  these,  Model  A  (after  Spengel)  is  constructed  on  the  same  prin- 
ciple as  the  Thoma-Jung  microtome.  The  knife-carrier  rests  on  thick 
plates  of  glass  in  place  of  metal.  The  knife  is  moved  by  means  of  a  crank. 
Model  B  (after  Schiefferdecker,  86)  is  peculiar  in  that  the  specimen 
to  be  cut  is  raised  by  a  micrometer  screw  in  a  vertical  rather  than  a  hori- 
zontal plane.  The  knife-carrier  runs  mechanically  on  horizontal  glass 
plates.  This  microtome  also  possesses  an  automatic  arrangement  for  the 
cutting  of  sections  of  equal  thickness,  so  that  when  the  micrometer  screw 
is  once  regulated  the  knife-holder  needs  only  to  be  moved  back  and  forth 


Fig.  6 — Diagram  showing  direction  of  the  movements  in  honing. 


to  make  sections  of  a  uniform  thickness.  With  the  help  of  both  models 
(A  and  B),  celloidin  as  well  as  paraffin  objects  can  be  cut.  Instruments 
giving  especially  good  results  in  the  serial  sectioning  of  paraffin  objects  are  : 
(i)  The  Minot  microtome,  which  can  be  obtained  from  Becker  and  from 
E.  Zimmermann  of  Leipzig  (Model  D,  Becker) .  Here  the  knife  is  station- 
ary, with  the  edge  of  the  blade  upward,  while  the  object  is  moved  up  and 
down  by  means  of  a  crank,  and  at  the  same  time  pushed  forward  toward 
the  blade.  The  thickness  of  the  section  is  regulated  automatically,  and 
by  merely  turning  the  wheel  a  long  series  of  sections  may  be  made  in 
a  short  time.  (2)  An  ingenious  and  well-built  instrument  is  the  im- 
proved rocking  microtome  of  R.  Jung,  in  Heidelberg  (Cambridge  rocking 
microtome).  The  knife  is  stationary,  with  the  edge  upward.  By 
means  of  a  clever  arrangement  the  object  is  advanced  toward  the  knife.  A 
lever  causing  a  slight  rotation  of  the  axis  upon  which  the  object  rests  moves 


38  THE    MICROSCOPIC    PREPARATION. 

the  object  up  and  down.  As  a  result,  every  section  has  not  a  plane  sur- 
face, as  is  the  case  with  other  microtomes,  but  appears  as  a  peripheral  sec- 
tion of  a  cylinder  the  radius  of  which  corresponds  to  the  distance  of  the 
blade  from  the  axis  bearing  the  object-holder.  (This  drawback  limits  the 
use  of  the  instrument. )  The  mechanism  has  one  advantage  :  excellent 
serial  sections  can  be  made,  having  a  thickness  of  only  i  p.  (vid.  Schieffer- 
decker,  92).  Bausch  &  Lomb,  of  Rochester,  N.  Y.,  make  excellent 
sliding  microtomes.  (Fig.  3.)  They  have  recently  constructed  for  Minot 
an  instrument  in  which  the  knife  is  fixed  at  both  ends.  The  object-car- 
rier is  elevated  by  a  screw,  and  moves  back  and  forth  under  the  knife. 

D.  THE  FURTHER  TREATMENT  OF  THE  SECTION* 

J.  FIXATION  TO  THE  SLIDE  AND  REMOVAL  OF  PARAFFIN. 

Sections  obtained  by  means  of  the  microtome  undergo  further  treat- 
ment either  loose  or,  better,  fixed  to  a  slide  or  cover-glass,  thus  making 
further  manipulation  much  easier. 

52.  The  simplest,  surest,  and  most  convenient  method  of  fixing  par- 
affin sections  to  the  slide  is  by  means  of  the  glycerin-albumen  of  P. 
Mayer  (83.2).     Egg-albumen  is  filtered  and  an  equal  volume  of  glycerin 
added.    To  prevent  decomposition  of  the  fluid  a  little  camphor  or  sodium 
salicylate  is  placed  in  the  mixture.     A  drop  of  this  fluid  is  smeared  on  the 
slide  or  cover-slip  as  evenly  and  thinly  as  possible.     A  section  or  a  series 
of  sections  arranged  in  their  proper  sequence  is  then  placed  upon  the  slide 
so  prepared.   Any  folds  in  the  section  are  smoothed  out  with  a  brush,  and 
the  section  or  the  whole  series  gently  pressed  down  upon  the  glass.   When 
the  desired  number  of  sections  are  on  the  slide  or  cover-slip,  they  are 
warmed  over  a  small  spirit  or  gas  flame  until  the  paraffin  is  melted.     At 
the  same  time  the  albumen  coagulates.     The  sections  are  now  fixed,  and 
are  loosened  from  the  glass  only  when  agents  are  used  which  dissolve 
albumen,  as,   for  instance,    strong  acids,  alkalies,   and  certain  staining 
fluids.     If  it  is  desired  that  a  given  space,  say  the  size  of  a  cover-slip,  be 
filled  up  with  sections  as  far  as  possible,  an  outline  of  the  cover-slip  to  be 
used  may  be  drawn  upon  a  piece  of  paper  and  placed  under  the  slide  in 
the  required  position. 

53.  A  second  and  in  many  respects  better  method  is  the  fixation  of 
the  section  with  distilled  water  (Gaule).     The  paraffin  sections  are 
spread  in  proper  sequence  on  a  thin  layer  of  water  placed  on  the  slide. 
There  should  be  sufficient  water  to  float  the  sections.     The  slide  is  then 
dried  in  a  warm  oven  kept  at  30°  to  35°  C.,  or  gently  heated  by  holding 
it  at  some  distance  from  a  spirit  or  gas  flame  (the  paraffin  should  not 
melt).     By  this  treatment  the  sections  are  entirely  flattened  out.     The 
superfluous  water  is  either  drained  off  by  tilting  or  drawn  off  with  blot- 
ting-paper,  the  sections  are  definitely  arranged  with  a  brush,  and  the 
whole  is  placed  for  several  hours  in  a  warm  oven  at  30°  to  35°  C.     The 
sections  thus  dried  are  exposed,  over  a  flame,  to  a  temperature  higher 
than  the  melting  point  of  the  paraffin,  and  from  now  on  can  be  subjected 
to  almost  any  after-treatment.     The  slide  or  cover-slip  should  be  thor- 
oughly cleaned  (preferably  with  alcohol  and  ether),  as  otherwise  the  water 
does  not  remain  in  a  layer,  but  gathers  in  drops. 

The  advantage  of  this  method  lies  in  the  fact  that  the  evaporated 
water  can  have  no  possible  influence  on  the  subsequent  staining  of  the 


THE    FURTHER    TREATMENT    OF    THE    SECTION.  39 

sections,  while  albumen,  especially  if  it  be  in  a  thick  layer,  is  sometimes 
stained,  thus  diminishing  the  transparency  of  the  preparation.  (For  fix- 
ation with  the  stain  vid.  T.  79.) 

This  method,  although  trustworthy  for  alcohol  and  sublimate  prepara- 
tions, often  fails  with  objects  that  have  been  treated  with  osmic  acid, 
chromic  acid  and  its  mixtures,  nitric  acid,  and  picrosulphuric  acid.  In 
such  cases  advantage  may  be  taken  of  the  so-called  Japanese  method, 
which  is  a  combination  of  the  above  fixation  methods.  A  little  Mayer's 
albumen  is  placed  on  the  slide  and  so  spread  about  that  hardly  a  trace  of 
the  substance  can  be  seen.  The  slide  is  then  put  in  a  warm  oven  heated 
to  7o°-C.  This  temperature  soon  coagulates  the  albumen,  after  which 
the  sections  are  fixed  to  the  slide  by  the  water  method  (Rainke,  95). 
The  procedure  can  be  varied  by  adding  to  the  distilled  water  one  drop  of 
glycerin-albumen  or  gum  arabic  to  every  30  c.c.  of  water  (vid.  also 
Nussbaum). 

When  a  large  number  of  paraffin  sections  are  to  be  fixed  to  cover-slips, 
the  following  method  may  be  recommended :  A  small  porcelain  evapo- 
rating dish  is  nearly  filled  with  distilled  water  and  placed  on  a  stand 
which  elevates  it  6  to  8  inches  from  the  table.  A  number  of  sec- 
tions are  placed  on  the  water,  which  is  then  heated  by  means  of  a  gas 
flame  until  the  sections  become  perfectly  flat,  care  being  taken  not  to 
raise  the  temperature  of  the  water  sufficiently  to  melt  the  paraffin .  Each 
section  is  then  taken  up  on  a  cover-slip  coated  with  a  very  thin  layer  of 
Mayer's  albumen  fixative.  During  this  procedure  the  cover-slips  are  held 
by  forceps,  and  the  sections  are  guided  by  means  of  a  small  camel' s-hair 
brush.  When  all  the  sections  have  thus  been  placed  on  cover-slips  they 
are  placed  for  four  to  six  hours  in  a  warm  oven  maintained  at  30°  to 
35°  C. 

54.  Celloidin  preparations  can  not  be  fixed  to  the  slide  with  the 
same  degree  of  certainty,  although  many  sections  may  be  treated  at  one 
time.  The  celloidin  sections  can  be  collected  in  their  sequence  on  strips 
of  paper  by  gently  pressing  such  a  strip,  on  the  blade  of  a  knife,  onto  the 
section  floating  in  the  alcohol.  The  sections  adhere  to  the  paper,  and  in 
this  way  the  entire  surface  of  the  strip  may  be  covered  by  series  of  sections. 
To  prevent  the  drying  of  the  sections,  a  number  of  such  strips  are  laid 
in  rows  on  a  layer  of  blotting-paper  moistened  with  70%  alcohol.  A  glass 
plate  of  corresponding  size  is  painted  with  very  fluid  celloidin.  After  the 
layer  of  celloidin  is  dry,  the  strips  of  paper  are  laid,  one  by  one,  on  the 
glass  plate,  with  sections  downward,  and  the  fingers  gently  passed  over 
the  reverse  side.  This  process  is  continued  until  the  entire  surface  of 
the  glass  is  covered.  On  carefully  raising  the  strips  it  is  seen  that  the 
sections  will  adhere  to  the  layer  of  celloidin.  (To  prevent  drying, 
sections  must  be  kept  moistened  with  70%  alcohol.)  After  first  drying 
the  sections  with  blotting-paper,  a  second  layer  of  very  thin  celloidin  is 
painted  on  the  surface  of  the  glass  plate.  When  this  layer  is  also  dry, 
the  plate  with  its  adherent  sections  is  placed  in  water.  Here  the  double 
layer  of  celloidin  containing  the  sections  is  separated  from  the  glass,  and 
is  ready  for  further  manipulation.  Before  mounting,  the  sheet  of  celloidin 
is  cut  with  scissors  into  convenient  portions. 

These  methods  of  fixation  are  of  especial  importance  in  the  prepa- 
ration of  series  of  sections.  By  this  we  mean  an  arrangement  of  the  sec- 
tions in  their  natural  sequence,  thus  making  it  possible  to  reconstruct  the 
object  from  the  sections.  It  is,  however,  advisable  to  fix  all  paraffin 


4O  THE    MICROSCOPIC    PREPARATION. 

sections  to  a  slide  or  cover-slip  before  subjecting  them  to  further  manip- 
ulation, even  though  the  regular  sequence  be  of  no  importance. 

55.  Removal  of  Paraffin. — Before  paraffin  sections,  either  fixed  or 
loose,  are  subjected  to  further  manipulation,  the  paraffin  surrounding  the 
tissues  must  be  removed.  This  may  be  done  by  means  of  several  agents 
having  a  solvent  action  on  paraffin,  such  as  xylol,  toluol,  oil  of  turpen- 
tine, etc.  After  the  paraffin  has  been  dissolved,  the  sections  are  trans- 
ferred to  absolute  alcohol  and  by  this  means  prepared  for  further  treatment 
with  aqueous  or  weak  alcoholic  solutions. 

In  the  case  of  celloidin  sections,  if  it  be  desirable  to  preserve 
the  surrounding  celloidin,  care  should  be  taken  that  the  preparations 
should  not  come  in  contact  with  any  agents  dissolving  celloidin.  These 
latter  are  alcohols  from  95  %  upward,  ether,  several  ethereal  oils,  especially 
oil  of  cloves,  but  not  the  oils  of  origanum,  cedar  wood,  lavender,  etc. 

2.  STAINING. 

It  is  in  most  cases  necessary  to  stain  tissues  to  bring  clearly  to  view 
the  tissue  elements  and  their  relation  to  each  other.  The  purpose  of 
staining  is  therefore  to  differentiate  the  tissue  elements.  The  differential 
staining  is  due  to  the  fact  that  certain  parts  of  the  tissue  take  up  more  stain 
than  others.  Staining  of  sections  may  be  looked  upon  as  a  microchemic 
color  reaction,  and  has  therefore  a  value  beyond  the  mere  coloring  of 
sections  so  that  they  may  be  seen  more  clearly. 

Broadly  speaking,  stains  used  in  microscopic  work  may  be  divided 
into  basic  stains,  which  show  special  affinity  for  the  nuclei  of  cells  and  are 
therefore  known  as  nuclear  stains,  and  acid  stains,  which  color  more 
readily  the  protoplasm — protoplasmic  stains.  Certain  stains,  which  we 
may  know  as  selective  stains  (they  maybe  either  basic  or  acid),  color  one 
tissue  element  more  vividly  than  others,  or  to  the  exclusion  of  others. 
Since  the  various  tissue  elements  show  affinity  for  different  stains,  prepa- 
rations may  be  colored  with  more  than  one  stain.  Accordingly  we  have 
simple,  double,  triple,  and  multiple  staining. 

Certain  stains  are  also  especially  adapted  for  staining  in  bulk  or  mass 
— that  is,  staining  a  piece  of  tissue  before  it  is  sectioned. 

SECTION  STAINING. 
Carmin.  —  56.    Aqueous    Borax  =  car  mi  n  Solution. — 8  gm.   of 

borax  and  2  gm.  of  carmin  are  ground  together  and  added  to  150  c.c. 
of  water.  After  twenty-four  hours  the  fluid  is  poured  off  and  filtered. 
The  sections,  previously  freed  from  paraffin  and  treated  with  alcohol,  are 
placed  in  this  fluid  for  several  hours  (as  long  as  twelve),  and  then  washed 
out  in  a  solution  of  0.5  to  i%  hydrochloric  acid  in  70%  alcohol. 
They  are  then  transferred  to  70%  alcohol. 

57.  Alcoholic    Borax=carmin    Solution. — 3  gm.   of  carmin  and 
4  gm.  of  borax  are  placed  in  93  c.c.  of  water,  after  which  100  c.c.  of 
70%  alcohol  is  added.     The  mixture  is  stirred,   then  allowed  to  settle, 
and  later  filtered.      Sections  are  treated  as  in  §  56. 

58.  Paracarmin  is  the  carmin  stain  containing  the  most  alcohol, 
and  is  therefore  of  great  value. 

Carminic  acid I      gm. 

Aluminium  chlorid 0.5     " 

Calcium  chlorid 4        " 

Alcohol,  IQ% 100     c.c. 


STAINING.  41 

Paracarmin  stains  quickly,  is  not  liable  to  overstain,  and  is  there- 
fore peculiarly  adapted  to  the  staining  of  large  objects.  Specimens  are 
washed  in  70%  alcohol,  with  the  addition  of  0.5%  aluminium  chlorid 
or  2.5%  glacial  acetic  acid  in  case  of  overstaining  (P.  Mayer,  92). 

59.  Czocor's  Cochineal  Solution. — 7  gm.  of  powdered  cochineal 
and  7  gm.  of  roasted  alum  are  kept  suspended  in  100  c.c.  of  water  by 
stirring  while  the  mixture  is  boiled  down  to  half  its  volume.      After 
cooling  it  is  filtered  and  a  little  carbolic  acid  added.     This  fluid  stains 
quite  rapidly  and  does  not  overstain.     Before  the  sections  are  placed  in 
alcohol  they  should  be  washed  with  distilled  water,  as  otherwise  the  alum 
is  precipitated  on  the  section  by  the  alcohol. 

Partsch  recommends  the  following  solution  of  cochineal :  Finely  pow- 
dered cochineal  is  boiled  for  some  time  in  a  5%  aqueous  solution  of 
alum,  and  filtered  on  cooling,  after  which  a  trace  of  hydrochloric  acid  is 
added.  It  stains  sections  in  two  to  five  minutes. 

60.  Alum-carmin  (Grenadier). — 100  c.c.  of  a  3%  to  5%  solution 
of  ordinary  alum,  or  preferably  ammonia-alum,  are  mixed  with  o.  5  gm.  to  i 
gm.  of  carmin,  boiled  for  one-fourth  of  an  hour,  and  after  cooling  filtered 
and  enough  distilled  water  added  to  replace  that  lost  by  evaporation.    This 
fluid  stains  quickly  but  does  not  overstain.     Wash  the  sections  in  water. 

Hematoxylin. — 61.  Bohmer's  Hematoxylin  : 

Hematoxylin  crystals .       i  gm. 

Absolute  alcohol 10  c.c. 

Potassium  alum 10  gm. 

Distilled  water 200  c.c. 

Dissolve  the  hematoxylin  crystals  in  the  alcohol,  and  the  alum  in  the  distilled  water. 
While  constantly  stirring,  add  the  first  solution  to  the  second. 

The  whole  is  then  left  for  about  fourteen  days  in  an  open  jar  or  dish  pro- 
tected from  the  dust,  during  which  time  the  color  changes  from  violet  to 
blue.  After  filtering,  the  stain  is  ready  for  use.  Sections,  either  loose  or 
fixed  to  the  slide  or  cover-slip,  are  placed  in  this  solution,  and  after  about 
half  an  hour  are  washed  with  water.  If  the  nuclei  are  well  stained  the  further 
treatment  with  alcohol  may  be  commenced.  Should  the  sections  be  over- 
stained,  a  condition  showing  itself  in  the  staining  of  the  cell -protoplasm 
as  well  as  the  nuclei,  the  sections  are  then  washed  in  an  acid  alcohol  wash 
(six  to  ten  drops  of  hydrochloric  acid  to  100  c.c.  of  70%  alcohol)  until 
the  blue  color  has  changed  to  a  reddish-brown  and  very  little  stain  comes 
from  the  section — usually  about  one  to  two  minutes.  They  are  then 
washed  in  tap -water,  and  passed  into  distilled  water  before  placing  in 
alcohol. 

62.  Delafield's  Hematoxylin: 

Hematoxylin  crystals 4  gm. 

Absolute  alcohol 25  c.c. 

Ammonia  alum,  saturated  aqueous  solution  400   " 

Alcohol,  95% 100  " 

Glycerin loo  " 

Dissolve  hematoxylin  crystals  in  absolute  alcohol  and  add  to  the  alum  solution,  after 
which  place  in  an  open  vessel  for  four  days,  filter,  and  add  the  95  %  alcohol  and  glycerin. 

After  a  few  days  it  is  again  filtered.  This  fluid  is  either  used  pure  or 
diluted  with  distilled  water.  Staining  is  the  same  as  with  Bohmer's  hema- 
toxylin. 


42  THE    MICROSCOPIC    PREPARATION. 

63.  Friedlander's  Glycerin-hematoxylin : 

Hematoxylin  crystals 2  gm. 

Potassium  alum      2    " 

Absolute  alcohol 100  c.c. 

Distilled  water .    .    .    .  100    " 

Glycerin 100    « 

Dissolve  the  hematoxylin  crystals  in  the  absolute  alcohol  and  the  alum  in  the  water ; 
mix  the  two  solutions  and  add  the  glycerin. 

The  mixture  is  filtered  and  exposed  for  several  weeks  to  the  air  and 
light,  until  the  odor  of  alcohol  has  disappeared,  and  then  again  filtered. 
It  stains  very  quickly.  Sections  are  afterward  washed  in  water  and  are 
placed  for  a  short  time  in  acid  alcohol  if  the  nuclei  are  to  be  especially 
brought  out. 

Ehrlich's  Hematoxylin : 

Hematoxylin  crystals 2  gm. 

Absolute  alcohol 60  c.c. 

Glycerin  "I     saturated  with     ....  60    " 

Distilled  water  j    ammonia  alum    ....  60    " 

Glacial  acetic  acid 3    " 

The  solution  is  to  be  exposed  to  light  for  a  long  time.  It  is  ready  for  use  when  it 
acquires  a  deep-red  color. 

Stain  as  above. 

64.  Hemalum   (P.   Mayer,   91). — i  gm.  of  hematein  is  dissolved 
by  heating  in  50  c.c.  of  absolute  alcohol.     This  is  poured  into  a  solu- 
tion of  50  gm.  of  alum  in   i  liter  of  distilled  water  and  the  whole  well 
stirred.     A  thymol   crystal   is  added  to  prevent  the  growth  of  fungus. 
The  advantages  of  hemalum  are  as  follows  :     The  stain  may  be  used  im- 
mediately  after    its    preparation,    it    stains    quickly,    never    overstains, 
especially  when  diluted  with  water,  and  penetrates  deeply,   making  it 
useful  for  staining  in  bulk.     After  staining,  sections  or  tissues  are  washed 
in  distilled  water. 

65.  Heidenhain's    Iron    Hematoxylin. — Good    results,    particu- 
larly in  emphasizing  certain  structures  of  the  cell  (centrosome),  are  ob- 
tained by  the  use  of  M.  Heidenhain's  iron  hematoxylin  (92.  2).     Tissues 
are  fixed  in  saline  sublimate  solutions  in  twelve  to  twenty-four  hours 
(vid.  T.  19),  after  which  they  are  washed  for  the  same  length  of  time  in 
running  water  and  then  placed  in  the  ascending  alcohols.     Very  thin  sec- 
tions  (in  case  of  amniota  not  over  4  /./.)  are  fixed   to  the  slide    with 
water  and' put  into  a  2.5%   aqueous  solution  of  ammonium  sulphate  of 
iron  for  four  to  eight  hours  (not  longer).     After  careful  rinsing  in  water, 
the  sections  are  brought  into  a  solution  of  hematoxylin  prepared  as  fol- 
lows:     Hematoxylin  crystals   i   gm.,  absolute  alcohol  10  c.c.,  and  dis- 
tilled water  90  c.c.     This  solution  should  remain  in  an  open  vessel  for 
about  four  weeks,   and,   before  using,   should  be  diluted  with  an  equal 
volume  of  distilled  water.      Staining  takes  place  in  twelve  to  twenty-four 
hours,  after  which  the  sections  are  rinsed  in  water  and  again  placed  in  a 
like  solution  of  ammonium  sulphate  of  iron,  until  black  clouds  cease  to  be 
given  off  from  the  sections.     They  are  rinsed  in  distilled  water,  passed 
through  alcohol  into  xylol,  and  mounted  in  balsam.      Should  a  protoplas- 
mic stain  be  desired,  rubin  in  weak  acid  solution  may  be  employed  (vid. 
also  M.  Heidenhain,  96). 

Coal-tar  or  anilin  stains. — Ehrlich  classifies  all  anilin  stains  as  salts 
having  basic  or  acid  properties.  The  basic  anilin  stains,  such  as  safra- 


STAINING. 


43 


nin,  methylene-blue,  methyl-green,  gentian  violet,  methyl -violet,  Bis- 
marck brown,  thionin,  and  toluidin-blue  are  nuclear  stains,  while  the 
acid  anilin  stains,  such  as  eosin,  erythrosin,  benzopurpurin,  acid  fuchsin, 
lichtgriin,  aurantia,  orange  G,  and  nigrosin  stain  diffusely  and  are  used  as 
protoplasmic  stains. 

66.  Safranin  : 

Safranin ,    .    .     I  gm. 

Absolute  alcohol 10  c.c. 

Anilin  water  .    .     • 90  •" 

Anilin  water  is  prepared  by  shaking  up  5  c.c.  to  8  c.c.  of  anilin  oil  in  100  c.c.  of 
distilled  water  and  filtering  through  a  wet  filter.  Dissolve  the  safranin  in  the  anilin 
water  and  add  the  alcohol.  Filter  before  using. 

Stain  sections  of  tissues  fixed  in  Flemming's  or  Hermann's  solutions 
for  twenty-four  hours,  and  decolorize  with  a  weak  solution  of  hydrochloric 
acid  in  absolute  alcohol  (i  :  1000).  After  a  varying  period  of  time  (usu- 
ally only  a  few  minutes)  all  the  tissue  elements  will  be  found  to  have 
become  bleached,  only  the  chromatin  of  the  nucleus  retaining  the  color. 

67.  Bismarck    Brown. — A  very   convenient    color   to   handle   is 
Bismarck  brown.      Of  this,  i  gm.  is  boiled  in  100  c.c.  of  water,  filtered, 
and  YZ  of  its  volume  of  absolute  alcohol  added.      Bismarck  brown  stains 
quickly  without  overstaining,  and  is  also  a  purely  nuclear  stain.     Wash 
in  absolute  alcohol. 

68.  Methyl-green   stains  very  quickly  (minutes),      i  gm.  is  dis- 
solved in  100  c.c.  of  distilled  water  to  which  25  c.c.  of  absolute  alcohol 
is  added.     Rinse  sections  in  water,  then  place  for  a  few  minutes  in  70% 
alcohol,  transfer  to  absolute  alcohol  for  a  minute,  etc. 

69.  Other   so-called   basic   anilin  stains    can  be  used  in  a  similar 
manner.     Thionin  or  toluidin-blue  in  dilute  aqueous  solutions  are  espe- 
cially useful.     Nuclei  appear  blue  and  mucus  red. 

70.  Double  Staining. — When  certain  stains  are   used  in  mixtures 
or    in    succession,  all  portions  of  the  section  are  not  stained   alike,  but 
certain  elements  take  up  one  stain,  others  another.     This  elective  affin- 
ity of  tissues  is  taken  advantage  of  in  plural  staining.     If  two  stains  are 
employed,  one  speaks  of  double  staining. 

71.  Picrocarmin  of  Ranvier. — Two  solutions  are  prepared,  a  satu- 
rated aqueous  solution  of  picric  acid  and  a  solution  of  carmin  in  ammonia. 
The  second  is  added  to  the  first  to  the  point  of  saturation.     The  whole  is 
evaporated  to  one-fifth  of  its  volume  and  filtered  after  cooling.     The 
solution  thus  obtained  is  again  evaporated  until  the  picrocarmin  remains 
in  the  form  of  a  powder.     A  i  fy  solution  of  the  latter  in  distilled  water 
is  the  fluid  used  for  staining. 

To  stain  with  this  solution,  one  or  two  drops  are  placed  on  the  slide 
over  the  object  and  the  whole  put  in  a  moist  chamber  for  twenty-four 
hours.  A  cover-slip  is  then  placed  over  the  preparation,  the  picrocarmin 
drained  off  with  a  piece  of  blotting-paper,  and  a  drop  of  formic-glycerin 
(i  :  100)  brought  under  the  cover-slip  by  irrigation.  Proper  differentia- 
tion takes  place  only  after  a  few  days,  and  the  acid-glycerin  may  then  be 
replaced  by  the  pure  glycerin.  In  objects  fixed  with  osmic  acid,  the 
nuclei  appear  red,  connective  tissue  pink,  elastic  fibers  canary  yellow, 
muscle  tissue  straw  color,  keratohyalin  red,  etc. 

72.  Weigert's  Picrocarmin. — The  preparation  of  Weigert's  picro- 
carmin is  somewhat  simpler.      2   gm.  of  carmin  are   stirred  in    4    c.c. 


44  THE    MICROSCOPIC    PREPARATION. 

of  ammonia  and  allowed  to  remain  -standing  in  a  well-corked  bottle 
for  twenty-four  hours.  This  is  mixed  with  200  c.c.  of  a  concentrated 
aqueous  solution  of  picric  acid  to  which  a  few  drops  of  acetic  acid  are 
added  after  another  twenty-four  hours.  The  result  is  a  slight  precipitate 
that  does  not  dissolve  on  stirring.  Filter  after  twenty-four  hours.  Should 
the  precipitate  also  pass  through  the  filter,  a  little  ammonia  is  added  to  dis- 
solve it.  Both  picrocarmin  solutions  dissolve  off  sections  fixed  to  the  slide 
with  albumen. 

73.  P.  Mayer's  Picric-magnesia=carmin. 

1.  Magnesia-carmin ; 

Carmin I  gm. 

Magnesia  usta o.i  " 

Distilled  water 20  c.c. 

2.  Picrate  of  magnesia  ; 

Carbonate  of  magnesia 0.25  gm. 

Picric  acid,  0.5%  in  distilled  water    .    .    .  200        c.c. 
Heat  to  boiling,  cool  and  filter. 

One  volume  of  the  first  solution  is  mixed  with  9  volumes  of  the 
second. 

Another  formula  is  magnesia -carmin  solution  i  volume,  magnesia- 
picrate  solution  4  volumes,  weak  magnesia-carmin  solution  5  volumes, 
magnesia  water  100  c.c.  The  latter  is  made  by  allowing  o.i  gm. 
of  magnesia  usta  to  remain  for  one  week  in  100  c.c.  of  water,  shaking 
from  time  to  time.  Sections  are  washed  in  either  distilled  or  magnesia 
water.  Staining  takes  place  quickly  ;  the  solution  may  be  used  for  stain- 
ing in  bulk. 

74.  Carmin-bleu  de  Lyon  (of  Rose). — Sections  or  pieces  of  tis- 
sue are  first  stained  with  carmin  (alum-  or  borax-carmin).      Bleu  de  Lyon 
is  dissolved  in  absolute  alcohol  and  diluted  with  the  latter  until  the  solu- 
tion is  of  a  light  bluish  color.      In  this  the  sections  or  pieces  of  tissue  are 
after-stained  for  twenty-four  hours  (developing  bone  stains,  for  instance, 
blue). 

75.  Picric  acid  is  often  used   as  a  secondary  stain,  either  in  aque- 
ous   (saturated  solution  diluted   i    to    3    times    in    water)   or  in   alco- 
holic solution   (weak  solutions  in  70%,  80%,    and   absolute   alcohol). 
Sections  previously  treated  with  carmin  or  hematoxylin  are  stained  for 
two  to  five  minutes,  washed  in  water  or  alcohol,  and  transferred  to  abso- 
lute alcohol,  etc.      Sections  stained  in  safranin  can  be  exposed  to  the  ac- 
tion of  an  alcoholic  picric  acid  solution.     A  solution  of  picric  acid  in 
70%    alcohol   may  be  used  to  wash  sections  stained  in  borax-carmin. 
This  often  gives  a  good  double  stain.     Sections  can  also  be  first  treated 
with  picric  acid  and  afterward  stained  with  alum -carmin. 

76.  Hematoxylin=eosin. — Sections  already  stained  in  hematoxylin 
are  placed  for  two  to  five  minutes  in  a  i  %  to  2  %  aqueous  solution  of 
eosin   or  in  a  i%  solution   of  eosin   in   60%  alcohol.     They  are  then 
washed  in  water  until  no  more  stain  comes  away,  after  which  they  remain 
for  only  a  short  time  in  absolute  alcohol. 

77.  Hematoxylin-safranin  of  Rabl    (85). — Sections  of  prepara- 
tions fixed  with   chromic -formic   acid  or    with  a  solution    of  platinum 
chlorid  are  stained  for  a  short  time  with  Delafield's  hematoxylin  (vid. 
T.  62),  then  counterstained  for  twelve  to  twenty-four  hours  with  safranin 
and  washed  with  absolute  alcohol  until  no  more  color  is  given  off. 


STAINING    IN    BULK.  45 

78.  Ehrlich-Biondi  Triple  Stain. — Of  the  many  triple  stains  in  use 
we  mention  only  the  most  important,  the  rubin  S — orange  G — methyl- 
green  mixture  of  Ehrlich  and  Biondi,  employed  according  to  the  modifi- 
cation of  M.  Heidenhain  (92.  2).     The  best  results  are  obtained  with 
objects  fixed  in  saline  sublimate  solution.    The  three  stains  just  mentioned 
are  prepared  in  concentrated  aqueous  solutions  (rubin  S  dissolves  in  the 
proportion  of  1:5,  orange  G  and  methyl -green  about  1:8).     These  con- 
centrated solutions  are  combined  in  the  following  volumes  :   rubin  S  4, 
orange  G  7,  methyl -green  8.   The  stock  solution  thus  obtained  is  diluted 
with  50  to  100  times  its  volume  of  distilled  water  before  using.     The  sec- 
tions should  be  as  thin  as  possible  and  fixed  to  the  slide  by  the  water 
method.     They  remain  for  twenty -four  hours  in  the  stain,  and  are  then 
washed  either  in  pure  90%  alcohol  or  in  such  with  the  addition  of  a  little 
acetic  acid  (i   to  2  drops  to  50  c.c. ),  until  the  rinsing  fluid  is  no  longer 
colored.      Before  staining  it  is  occasionally  of  advantage   to   treat   the 
sections  with  acetic  acid  (2  :  1000)  for  one  to  two  hours. 

79.  P.  Mayer  (96)  advises  fixation  of  the  sections  to  the  slide  with 
the  staining  solution  instead  of  water.      On  heating  the  slide  the  sections 
stain  very  energetically,  and  results  are  obtained  which  would  otherwise 
be  difficult  to  produce.    Before  the  sections  are  placed  in  xylol  to  remove 
the  paraffin,  they  must  be  thoroughly  dried. 

STAINING  IN  BULK. 

Instead  of  staining  in  sections,  entire  objects  can  be  stained  before 
cutting.  This  method  is  in  general  much  slower,  and  demands,  there- 
fore, special  staining  solutions,  as,  for  instance  : 

80.  Alcoholic     borax-carmin    solution    (vid.    T.     57). — Pieces     ^ 
cm.  in  diameter  remain  in  the  stain  at  least  twenty-four  hours,  are  then 
decolorized   for  the  same  length   of  time  in  acid  alcohol  (0.5%  to   i% 
hydrochloric  acid  in  70%   alcohol),  and  after  washing  in  70^?  alcohol 
are  transferred  to  90%  alcohol.      Larger  objects  require  a  correspondingly 
longer  time. 

81.  Paracarmin. — Treatment  as  in  section  staining,   length  of  time 
according  to  size  of  object  (vid.  T.  58). 

82.  Alum-carmin  of  Grenacher  (vid.  T.  60).    This  never  overstains. 
Time  of  staining  according  to  size  of  object.     Wash  in  water,  then  trans- 
fer to  70%  and  90%  alcohol. 

83.  Hemalum  (vide  T.  64),  when  diluted  with  water,  is  very  useful 
for  staining  in  bulk.     After  staining,  objects  should  be  washed  with  dis- 
tilled water. 

84.  Bohmer's  hematoxylin   (vid.   T.    61)   stains   small   pieces  very 
sharply.      Use  the  same  as  hemalum. 

85.  Hematoxylin  staining  according  to  R.  Heidenhain' s  method  is 
especially  recommended  for  staining  in  bulk. 

Stain  objects  fixed  in  alcohol  or  picric  acid  twenty-four  hours  in  a 
°-33%  aqueous  solution  of  hematoxylin  ;  transfer  for  an  equal  length  of 
time  to  a  0.5%  aqueous  solution  of  potassium  chromate,  changing  often 
until  the  color  ceases  to  run.  Wash  with  water  and  pass  into  strong 
alcohol.  This  stain  also  colors  the  protoplasm,  and  is  so  powerful  that 
very  thin  sections  are  an  absolute  condition  to  the  clearness  of  the  prepa- 
ration. 


46 


THE    MICROSCOPIC    PREPARATION. 


86.  If  the  objects  have  been  fixed  with  picric  acid  and  the  latter  has 
not  been  entirely  washed  out,  staining  in  bulk  by  the  above  methods  pro- 
duces very  striking  differentiation. 

87.  Pieces  of  tissue  stained  in  bulk  may  be  infiltrated,  imbedded, 
and  cut  according  to  the  ordinary  methods.     Under  these  circumstances, 
section  staining  is  not  necessary  unless  a  still  further  differentiation  be 
desired. 

88.  In  general,  then,  the  treatment  of  the  object  is  somewhat  as  fol- 
lows :   First,  it  is  fixed  in  some  one  of  the  fixing  fluids  already  described, 
then  carefully  washed,  and  in  certain  cases  stained  in  bulk  before  infiltrat- 
ing with  paraffin  or  celloidin  ;  or  the  staining  may  be  postponed  until 
the  tissue  has  been  cut.     In  the  latter  case,  the  sections  are  subjected  to 
the  stain  either  loose  or  fastened  to  the  slide  or  cover-slip. 

89.  In  all  cases  it  is  absolutely  essential  that  the  paraffin  be  entirely 
removed.     After  the  sections  have  been  stained  and  washed,  they  are 
transferred  to  absolute  alcohol  in  case  it  be  desired  to  mount  them  in 
some    resinous   medium.     They    may  also  be    mounted  in    glycerin   or 
acetate  of  potash,  into  which  they  may  be  passed  directly  from  distilled 
water. 

90.  The  method  of  staining  tissues  in  sections  or  in  bulk  is  shown  in 
the  following  diagrams : 


In  Bulk. 
go%  alcohol 


Water 


In  Sections, 

Celloidin  sections      Paraffin  sections 
in  90  %  alcohol  I 

Remove  paraffin 


Stain  > 


Distilled 
water 


s 

Wash  in  water 

s, 

Wash  in  acid  alcohol 

1 

4- 

70  f0  alcohol 

70%  alcohol 

Absolute  alcohol 


Absolute  alcohol 

gofc  alcohol 

j-t 
Distilled  water 


70  #    alco- 
hoi 


70%   alco- 
hol 


Absolute  alcohol 


E.  PREPARATION  OF  PERMANENT  SPECIMENS. 

The  resinous  media  used  in  the  final  mounting  of  preparations  are 
Canada  balsam  and  damar. 

91.  Commercial  Canada  balsam  is  usually  dissolved  in  turpentine  ;  it 
should  be  slowly  evaporated  in  casserole  and  then  dissolved  in  xylol, 
toluol,  or  chloroform,  etc.  The  proper  concentration  of  the  solution 
is  found  with  a  little  experience.  A  thick  solution  penetrates  the  in- 


PREPARATION    OF    PERMANENT    SPECIMENS.  47 

terstices  of  the  section  with  difficulty,  and  usually  contains  air-bubbles 
which  often  hide  the  best  areas  of  the  preparation,  and  can  only  be  re- 
moved with  difficulty  by  heating  over  a  flame.  Thin  solutions,  on  the 
other  hand,  have  also  their  disadvantages  ;  they  evaporate  very  quickly,  and 
the  empty  space  thus  created  between  the  cover-slip  and  slide  must  again 
be  filled  with  Canada  balsam.  This  is  best  done  by  dipping  a  glass  rod 
into  the  solution  and  placing  one  drop  at  the  edge  of  the  cover-slip, 
whereupon  the  fluid  spreads  out  between  the  cover-slip  and  slide  as  a 
result  of  capillary  attraction.  Canada  balsam  dries  rather  slowly,  the 
rapidity  of  the  process  depending  upon  the  temperature  of  the  room.  To 
dry  quickly,  the  slides  may  be  held  for  a  few  moments  over  a  gas  or 
alcohol  flame,  or  they  may  be  placed  in  a  warm  oven,  where  the  prepara.- 
tions  become  so  dry  in  twenty-four  hours  that  they  can  be  examined  with 
an  oil-immersion  lens.  The  oil  used  for  this  purpose  should  be  wiped 
away  from  the  cover-slip  after  examination.  This  can  only  be  done,  with- 
out moving  the  cover-slip,  when  the  balsam  is  thoroughly  dry  and  holds 
the  cover-slip  firmly  in  place. 

92.  Damar  is  dissolved  preferably  in  equal  parts  of  oil  of  turpentine 
and  benzin.      It  has  the  advantage  of  not  rendering  the  preparation  as 
translucent  as  does  Canada  balsam.     Otherwise  it  is  used  as  the  latter. 

93.  Since  alcohol  does  not  mix  with  Canada  balsam  and  damar,  an 
intermediate  or  clearing  fluid  is  used  in  transferring  objects   from  the 
former  into  the  latter.      Xylol,  toluol,  carbol-xylol  (xylol,  3  parts ;    car- 
bolic acid,  i   part),  oil  of  bergamot,  oil  of  cloves,  and  oil  of  origanum 
are  ordinarily  used. 

94.  The  process  is  somewhat  simpler  where   sections  are  fixed  to 
the  slide.     Xylol  is  dropped  onto  the  surface  of  the  slide,  or  better, 
the  whole  preparation  is  placed  for  a  few  minutes  in  a  vessel  containing 
xylol  until  the  diffusion  currents  have  ceased  (which  may  be  seen  with 
the  naked  eye).     The  slide  is  then  taken  out,  tilted  to  allow  the  xylol  to 
run  off,  wiped  dry  around  the  object  with  a  cloth,  and  placed  upon  the 
table  with   the  specimen  upward.     A   drop   of  Canada  balsam  is  now 
placed  on  the  section  (usually  on  its  left  side),  and  a  clean  cover -slip 
grasped  with  a  small  forceps.     It  is  then  gently  lowered  in  such  a  way 
that  the  Canada  balsam  spreads  out  evenly  and  no  air-bubbles  are  im- 
prisoned under  the  glass.     When  this  is  done  the  preparation  is  finished. 

95.  If  one  is  dealing  with  loose  sections,  a  spatula  or  section-lifter  is 
very  useful  in  transferring  them  from  absolute  alcohol  into  the  clearing 
fluid — carbol-xylol  or  bergamot  oil  (xylol  evaporates  very  rapidly) — and 
from  this  onto  the  slide.      In  doing  this  it  is  necessary  that   the  sec- 
tion should  lie  well  spread  out  on  the  section -lifter,  wrinkles  being  re- 
moved with  a  needle  or  small  camel' s-hair  brush.      In  sliding  the  section 
off  the  spatula  (with  a  needle  or  brush)  a  small  quantity  of  the  clearing  fluid 
is  also  brought  onto  the  slide.     This  must  be  removed  as  far  as  possible 
by  tilting  or  with  blotting-paper.     The  section  can  now  be  mounted 
in   Canada  balsam  as  before.      For  esthetic  and  practical   reasons   the 
student  should  see  that  during  the  spreading  of  the  drop  of  Canada  balsam 
the  section  remains  under  the  middle  of  the  cover-slip.     Should  it  float 
to  the  edge,  it  is  best  to  raise  the  cover-slip  and  lower  it  into  place  again. 
The  cover-slip  should  never  be  slid  over  the  specimen. 

97.  To  mount  in  glycerin  or  acetate  of  potash  (33%  solution  in  dis- 
tilled water),  the  sections  are  transferred  from  water  to  the  slide,  covered 


48  THE    MICROSCOPIC    PREPARATION. 

with  a  drop  of  glycerin  or  acetate  of  potash,  and  the  cover-slip  applied. 
These  methods  are  employed  in  mounting  sections  colored  with  a  stain 
that  would  be  injured  by  contact  with  alcohol,  and  where  clearing  is  not 
especially  necessary. 

98.  Farrant's  Gum  Glycerin. 

In  place  of  pure  glycerin  the  following  mixture  may  be  used  : 

Glycerin      5°  c-c- 

Water      50    " 

Gum-arabic  (powder) 50  gm. 

Arsenious  acid I    " 

Dissolve  the  arsenious  acid  in  water.  Place  the  gum-arabic  in  a  glass  mortar  and 
mix  it  with  the  water ;  then  add  the  glycerin.  Filter  through  a  wet  filter-paper  or 
through  fine  muslin. 

99.  To  preserve  such  preparations  for  any  length  of  time  the  cover- 
glasses  must  be  so  fixed  as  to  shut  off  the  glycerin  or  acetate  of  potash 
from  the  air.     For  this  purpose  cements  or  varnishes  are  employed  which 
are  painted  over  the  edges  of  the  cover-slip.     These  masses  adhere  to  the 
glass,  harden,  and  fasten  the  cover-slip  firmly  to  the  slide,  hermetically 
sealing  the  object.     The  best  of  these  is  probably  Kronig's  varnish,  pre- 
pared as  follows  :    2    parts    of  wax   are    melted    and  7    to   9  parts   of 
colophonium  stirred  in,   and  the  mass  filtered  hot.      Before  employing 
an  oil -immersion  lens  it  is  advisable  to  paint  the  edge  with  an  alcoholic 
solution  of  shellac. 

F.  INTRODUCTION  TO  METHODS  OF  INJECTION. 

100.  A  few  remarks  on  the  injection  of  the  vascular  system  will  not 
here  be  amiss,  as  it  is  only  by  this  method  that  the  relations  of  the  blood- 
vessels to  the  neighboring  tissue  elements  can  be  clearly  brought  out. 
The  process  consists  in  filling  the  vessels  with  a  mass  that  can  be  injected 
in  a  fluid  state  but  hardens  readily,  and  is  at  the  same  time  suitable  for 
microscopic  purposes  and  for  sectioning  methods.      Of  such  substances 
there  are  a  large  number,  and  the  technic  of  injection  has  been  developed 
to  such  a  degree  that  it  has  become  a  very  important  part  of  anatomic 
technic  in  general.      Gelatin  masses  of  different  composition  have  come 
into  general  use  for  injecting  the  vascular  system  ;  of  these,  we  shall  here 
mention  a  red  and  a  blue  mass. 

101.  Gelatin=carmin. — The  first  is  a  gelatin -carmin  mass,  and  is 
prepared  as   follows:      (i)   4  gm.  of  carmin  are  stirred  into  8  c.c.  of 
water  and  thoroughly  ground.     Into  this  a  sufficient  quantity  of  ammonia 
is  poured  to  produce  a  dark  cherry  color  and  render  the  whole  transpar- 
ent.     (2)   50  gm.  of  finest  quality  gelatin  is  placed  in  distilled  water  for 
twelve  hours  until  well  soaked.     It   is   then   pressed  out  by  hand  and 
melted  at  a  temperature  of  70°  C.  in  a  porcelain  evaporating  dish.     The 
two  solutions  are  now  slowly  mixed,  the  whole  being  constantly  stirred 
until  a  complete  and  homogeneous  mixture  is  obtained.     To  this  mass  is 
added,  drop  by  drop,  a  25%  acetic  acid  solution  until  the  color  begins 
to  change  to  a  brick  red  and  the  mass  becomes  slightly  opaque.     This 
should  be  very  carefully  done,  as  a  single  drop  too  much  may  spoil  the 
whole.      During  this  procedure  the  substance  should  be  kept  at  70°  C. 
and  constantly  stirred.     The  change  in  color  indicates  that  the  reaction 
of  the  mass  has  become  neutral  or  even  slightly  acid  (an  ammoniac  solu- 
tion should  not  be  used,  since  the  stain  diffuses  through  the  wall  of  the 


INTRODUCTION    TO    METHODS   OF    INJECTION.  49 

vessel  and  colors  the  surrounding  tissues)  ;   the  whole  is  filtered  through 
flannel  while  still  warm. 

1 02.  The  blue  mass  is  prepared  from  an  aqueous  solution  of  Berlin 
blue.     A  saturated  solution  is  made  and  poured  (as  above)  into  a  solution 
of  gelatin  warmed  to  70°  C.   until  the  desired  intensity  of  color  is  ob- 
tained. 

103.  Injection  masses  already  prepared  are  to  be  had  in  commerce. 
Besides  those  already  mentioned,  still  others  colored  with  China  ink,  etc. , 
are  in  general  use. 

104.  Small  animals  are  injected  as  a  whole  by  passing  the  cannula  of 
a  syringe  into  the  left  ventricle  or  aorta.      In  the  case  of  large  animals, 
or  where  very  delicate  injections  are  to  be  made,  the  cannula  is  inserted 
into  one  of  the  vessels  of  the  respective  organs.      The  proper  ligation  of 
the  remaining  vessels  should  not  be  omitted. 

105.  Before  injecting,  the  animals  or  organs  are  kept  warm  in  water 
heated  to  about  38°  C.  in  order  to  prevent  the  injection  mass  from  hard- 
ening before  passing  into  the  smaller  vessels. 

106.  Before  injecting,  it  is  always  desirable  to  thoroughly  bleed  the 
animal,  or  press  out  as  carefully  as  possible  all  the  blood  contained  in  the 
organ. 

107.  Organs  injected  with  carmin  are  fixed  in  alcohol  and  should  not 
be  brought  in  contact  with  acids  or  alkalies.      Such  parts  as  are  injected 
with  Berlin  blue  are  less  sensitive  in  their  after-treatment.      Pieces  or  sec- 
tions that  have  become  pale  regain  their  blue  color  in  oil  of  cloves. 

108.  If  objects  or  sections  injected  with  Berlin  blue  be  treated  with 
a  solution    of  palladium    chlorid,   the  bluish    color  changes    to   a   dark 
brown  which  afterward  remains  unchanged  (Kupffer). 

109.  In  thin  membranes  and  sections  the  vessel -walls  can  be  rendered 
distinct  by  silver-impregnation,  which  brings  out  the  outlines  of  their  en- 
dothelial  cells.     This  may  be  done  either  by  injecting  the  vessel  with  a 
i%    solution   of  silver  nitrate,  or,  according  to  the  process  of  Chrzon- 
szczewsky,    with   a    0.25%    solution  of  silver  nitrate  in  gelatin.     This 
method  is  of  advantage,  since,  after  hardening,  the  capillaries  of  the  in- 
jected tissue  appear  slightly  distended.      Organs  thus  treated  can  be  sec- 
tioned, but  the  endothelial  mosaic  of  the  vessels  does  not  appear  definitely 
until  the  sections  have  been  exposed  to  sunlight. 

no.  By  means  of  the  above  injection  methods  other  lumina  can  be 
filled,  as,  for  instance,  those  of  the  glands.  As  a  rule,  these  are  only  par- 
tially filled,  since  they  end  blindly,  and  their  walls  are  less  resistant  and 
may  be  damaged  by  the  pressure  produced  by  the  injection. 

in.  The  injecting  of  lymph -channels,  lymph -vessels,  and  lymph- 
spaces  is  usually  done  by  puncture.  A  pointed  cannula  is  thrust  into 
the  tissue  and  the  syringe  emptied  by  a  slight  but  constant  pressure.  The 
injected  fluid  spreads  by  means  of  the  channels  offering  the  least  resist- 
ance. For  this  purpose  it  is  best  to  employ  aqueous  solutions  of  Berlin 
blue  or  silver  nitrate,  as  the  thicker  gelatin  solutions  cause  tearing  of  the 
tissues. 

112.  To  bring  out  the  blood  capillaries  and  the  lymphatic  channels, 

Altman's  process  (79),  in  which  the  vessels  are  injected  with  olive  oil,  is 

useful.     The    objects   are   then   treated  with  osmic  acid,    sectioned   by 

means  of  a  freezing  microtome,  and  finally  treated  with  eau  de  Javelle 

4 


5<D  THE    MICROSCOPIC    PREPARATION. 

(a  concentrated  solution  of  hypochlorite  of  potassium).  By  this  process 
all  the  tissues  are  eaten  away,  the  casts  of  the  blood-vessels  remaining  as  a 
dark  framework  (corrosion).  The  manipulation  of  these  preparations  is 
extremely  difficult  on  account  of  the  brittleness  of  the  oil  casts.  For 
lymph-channels  Altman  {ibid.)  used  the  so-called  oil -impregnation. 
Fresh  pieces  of  tissues,  thin  lamellae  of  organs,  cornea,  etc.,  are  placed 
for  five  to  eight  days  in  a  mixture  containing  olive  oil  i  part,  absolute 
alcohol  ^  part,  sulphuric  ether  ^  part  (or  castor  oil  2,  absolute  alcohol 
i,  etc.).  The  pieces  are  then  laid  for  several  hours  in  water,  where 
the  externally  adherent  globules  of  oil  are  mechanically  removed  and 
those  in  the  lymph -canalicular  system  are  precipitated.  The  objects  are 
now  treated  with  osmic  acid,  cut  by  means  of  a  freezing  microtome, 
and  corroded.  In  this  case,  the  corrosive  fluid  (eau  de  Javelle)  should 
be  diluted  two  or  three  times. 


GENERAL  HISTOLOGY. 
I.  THE  CELL. 

DURING  the  latter  part  of  the  seventeenth  century,  Hooke,  Mal- 
pighi,  and  Grew,  making  observations  with  the  simple  and  imperfect 
microscopes  of  their  day,  saw  in  plants  small  compartment-like 
spaces,  surrounded  by  a  distinct  wall  and  filled  with  air  or  a  liquid  ; 
to  these  the  name  cell  was  applied.  These  earlier  observations  were 
extended  in  various  directions  during  the  latter  part  of  the  seven- 
teenth and  the  eighteenth  century.  Little  advance  was  made, 
however,  until  Robert  Brown  (1831)  directed  attention  to  a  small 
body  found  in  the  cell,  previously  mentioned  by  Fontana,  and 
known  as  the  nucleus.  In  the  nucleus  Valentin  observed  (1836) 
a  small  body  known  as  the  nucleolus.  In  1838  Schleiden  brought 
forward  proof  to  show  that  plants  were  made  up  wholly  of  cells, 
and  especially  emphasized  the  importance  of  the  nuclei  of  cells.  In 
1839  Schwann  originated  the  theory  that  the  animal  body  was 
built  up  of  cells  resembling  those  described  for  plants.  Both 
Schleiden  and  Schwann  defined  a  cell  as  a  small  vesicle,  surrounded 
by  a  firm  membrane  inclosing  a  fluid  in  which  floats  a  nucleus. 
This  conception  of  the  structure  of  the  cell  was  destined,  however, 
to  undergo  important  modification.  In  1846  v.  Mohl  recognized  in 
the  cell  a  semifluid,  granular  substance  which  he  named  protoplasm. 
Other  investigators  (Kolliker  and  Bischoff)  observed  animal  cells 
devoid  of  a  distinct  cell  membrane.  Max  Schultze  (1861)  attacked 
vigorously  the  older  conception  of  the  structure  of  cells,  proclaim- 
ing the  identity  of  the  protoplasm  in  all  forms  of  life,  both  plant  and 
animal,  and  the  cell  was  defined  as  a  nucleated  mass  of  protoplasm 
endo^vcd  with  the  attributes  of  life.  In  this  sense  the  term  cell  is 
now  used. 

The  simplest  forms  of  animal  life  are  organisms  consisting  of 
only  one  cell  (protozoa).  Even  in  the  development  of  the  higher 
animals,  the  first  stage  of  development,  the  fertilized  egg,  is  a  single 
cell.  This  by  repeated  division  gives  rise  to  a  mass  of  similar  cells, 
which,  owing  to  their  likeness  in  shape  and  structure,  are  said  to  be 
undifferentiated.  As  development  proceeds,  the  cells  of  this  mass 
arrange  themselves  into  three  layers,  the  germ  layers,  the  outer  one 
of  which  is  the  ectoderm,  the  middle  one  the  mesoderm,  and  the  inner 
one  the  entoderm.  In  the  further  development,  the  cells  of  the 
germ  layers  change  their  form,  assume  new  qualities,  adapting 


£2  THE    CELL. 

themselves  to  perform  certain  definite  functions  ;  a  division  of  labor 
ensues, — the  cells  become  differentiated.  Cells  having  similar  shape 
and  similar  function  are  grouped  to  form  tissues,  and  tissues  are 
grouped  to  form  organs. 

We  shall  now  consider  the  structure  of  the  cell.      Every  cell 
consists  of  a  cell-body  and  a  nucleus. 


A.  THE  CELL-BODY. 

The  body  of  the  cell  consists  of  a  substance  known  as  proto- 
plasm  or    cytoplasm.     This  is    not    a    substance  having   uniform 


Vacuoles. 


Chromatin  network. 

Linin  network. 
Nuclear  fluid. 

Nuclear  membrane. 
Cell-membrane. 


Exoplasm. 


Spongioplasm. 
Hyaloplasm. 

Nucleolus. 
Chromatin  net-knot. 

Centrosome. 
Centrosphere. 


Foreign  inclosures.     Metaplasm. 
Fig.  7. — Diagram  of  a  cell. 

physical  and  chemical  qualities,  but  a  mixture  of  various  organic 
compounds  concerning  which  knowledge  is  not  as  yet  conclusive, 
but  which  in  general  are  proteid  bodies  or  albumins  in  the  widest 
sense. 

In  spite  of  the  manifold  differences  in  its  composition,  proto- 
plasm exhibits  certain  general  fundamental  properties  which  are 
always  present  wherever  it  is  found.  Ordinarily,  protoplasm  ex- 
hibits certain  structural  characteristics.  In  it  are  observed  two  con- 
stituents,— threads  or  plates,  which  are  straight  or  winding,  which 
branch,  anastomose,  or  interlace,  and  which  are  generally  arranged  in 
a  regular  framework,  network,  or  reticulum.  These  threads  probably 
consist  of  small  particles  arranged  in  rows,  called  cell-microsomes 
(yid.  van  Beneden,  83  ;  M.  Heidenhain,  94  ;  and  others).  This  sub- 


THE    CELL- BODY.  53 

stance  is  known  as  protoplasm  in  the  stricter  sense  (Kupffer,  75)  ;  also 
as  spongioplasm,  or  the  fibrillar  mass  of  Flemming  (82).  The  other 
constituent  of  the  cytoplasm  is  a  more  fluid  substance  lying  between 
the  threads  in  the  meshes  of  the  spongioplastic  network,  and  is 
known  as  paraplasm  (Kupffer),  hyaloplasm,  cytolymph,  or  the 
interfibrillar  substance  of  Flemming. 

According  to  most  investigators,  the  more  important  vital  pro- 
cesses of  the  cell  are  to  be  identified  with  the  spongioplasm,  and 
are  controlled  by  the  nucleus,  while  the  paraplasm  assumes  an 
inferior  or  passive  role. 

Protoplasm  displays  phenomena  of  motion,  shown  on  the  one 
hand  by  contraction,  and  on  the  other  by  the  formation  of  processes 
that  take  the  form  either  of  blunt  projections  or  lobes,  or  of  long, 
pointed,  and  even  branched  threads  or  processes  known  as  pseudo- 
podia.  The  extension  and  withdrawal  of  the  pseudopodia  enable  the 
cell  to  change  its  position.  The  point  of  such  a  process  fastens  to 
some  object  and  the  rest  of  the  cell  is  drawn  forward,  thus  giving  the 
cell  a  creeping  motion — wandering  cells.  Certain  cells  take  up  and 
surround  foreign  bodies  by  means  of  their  pseudopodia.  If  these 


_  Cilia. 


Fig.  8. — Cylindric  ciliated  cells  from  the  primitive  kidney  of  Petromyzon planeri ; 

XI200. 

bodies  are  suitable  for  nutrition,  they  are  assimilated  ;  if  not,  they 
can,  under  certain  circumstances,  be  deposited  by  the  cell  in  cer- 
tain localities  (Metschnikoff's  phagocytes).  Similar  thread-like 
processes  which,  however,  can  not  be  drawn  into  the  cell,  occur  in 
some  cells  in  the  shape  of  cilia,  which  are  in  constant  and  energetic 
motion — ciliated  cells.  Certain  cells  possess  only  a  single  long  pro- 
cess, by  means  of  which  unattached  cells  are  capable  of  direct  or 
rotating  motion — -flagellate  cells,  spermatozoa. 

Inside  of  the  cell-body  the  protoplasm  also  shows  phenomena  of 
motion,  the  streaming  of  the  protoplasm.  In  plant  cells  there  is 
often  a  noticeable  regularity  in  the  direction  of  the  current.  Men- 
tion should  not  be  omitted  of  the  so-called  molecular  or  Brownian 
movement  in  the  cells,  which  consists  in  a  rapid  whirling  motion 
of  particles  or  granules  suspended  in  the  protoplasm  (Brown). 

Living  protoplasm  is  irritable  in  the  highest  degree,  and  reacts 
very  strongly  to  chemic  and  physical  agents.  It  is  very  sensitive  to 
changes  in  temperature.  All  the  phenomena  of  life  occur  in  greater 
intensity  and  more  rapidly  in  a  warm  than  in  a  cold  temperature, 


54  THE    CELL. 

this  fact  being  very  strikingly  shown  by  the  phenomena  of  motion 
in  the  cell,  as  also  in  its  propagation.  By  subjecting  protoplasm  to 
different  temperatures,  its  various  movements  can  be  slowed  or 
quickened.  It  dies  in  too  high  or  too  low  a  temperature. 

Certain  substances  coming  in  contact  with  the  cell  from  a  given  direc- 
tion have  on  it  an  attracting  or  repelling  action.  These  phenomena  are 
known  as  positive  and  negative  chemotropism  (chemotaxis) .  The  action 
of  chemic  agents  on  the  different  wandering  cells  of  the  body  and  on  cer- 
tain free-swimming  unicellular  organisms  naturally  varies  to  a  great 
degree.  Among  these  phenomena  must  be  included  those  produced  by 
water  (hydrotropism)  and  light  (heliotropism).  It  is  very  probable  that 
all  these  phenomena  are  of  importance  to  the  proper  appreciation  of  some 
of  the  processes  going  on  in  the  vertebrate  body  (as,  for  instance,  in  the 
origin  of  diseases  caused  by  micro-organisms). 

Protoplasm  may  contain  various  structures.  Of  these,  the 
vacuolcs  deserve  special  mention.  They  are  more  or  less  sharply 
defined  cavities  filled  with  fluid,  and  vary  considerably  in  number 
and  size.  The  fluids  that  they  contain  differ  somewhat,  but  are 
alwrays  secreted  by  the  protoplasm,  and  are,  as  a  rule,  finally  emp- 
tied out  of  the  cell.  As  a  consequence,  vacuoles  are  best  studied 
where  the  function  of  the  cell  is  a  secretory  one.  Here  they  are 
often  large,  and  sometimes  fill  up  the  whole  cell,  the  contents  of 
which  are  then  emptied  out  {glandular  cells). 

Contents  of  a  solid  nature,  such  as  fat,  pigment,  glycogen,  and 
crystals,  are  peculiar  to  certain  cells.  By  these  deposits  the 
cell  is  more  or  less  changed,  the  greatest  variation  in  form  taking 
place  in  the  production  of  fat.  The  latter,  as  a  rule,  takes  the  shape 
of  a  globule,  and  greatly  modifies  the  position  of  the  normal  con- 
stituents of  the  cell.  Deposits  of  pigment  alter  the  cells  to  a  less 
degree.  This  substance  occurs  in  the  protoplasm  either  in  solution 
or  in  the  form  of  fine  crystalline  bodies.  Glycogen  is  more  gener- 
ally diffused,  occurring  very  generally  in  embryonal  cells  and  in  the 
liver-  and  cartilage-cells  of  the  adult.  Occasionally  we  find  larger 
crystals  in  animal  cells,  as,  for  instance,  in  the  red  blood-corpuscles 
of  the  teleosts.  So-called  margarin  crystals  sometimes  occur  in 
large  numbers  as  stellate  figures  in  dead  fatty  tissues  kept  at  low 
temperatures. 

By  employing  certain  methods  the  existence  of  granules  can 
generally  be  demonstrated  in  protoplasm.  Some  authors  even  refer 
the  vital  qualities  of  protoplasm  to  these  particular  bodies  (Alt- 
mann's  bioblasts,  94). 

In  some  cases  the  outer  layer  of  the  cell-protoplasm  shows  dif- 
ferentiation, leading  to  the  formation  of  a  distinct  cell-membrane  (as 
in  fat-cells,  cartilage-cells,  goblet-cells,  etc.).  F.  E.  Schulze  has  given 
it  the  name  pellicula  in  cases  where  the  entire  cell  is  surrounded  by 
a  homogeneous  layer,  and  cuticula  or  cuticle  where  only  one  side  of 
the  cell  is  supplied  with  the  membrane  (as  in  the  intestinal  epithe- 


THE    NUCLEUS.  55 

Hum).      It   is   assumed  that  both  spongioplasm  and  paraplasm  are 
concerned  in  the  formation  of  this  membrane. 

In  the  protoplasm  of  many  cells  there  is  found  a  small  body 
known  as  the  centrosome.  This  is  usually  situated  near  the  nucleus 
of  the  cell,  occasionally  in  the  nucleus.  Generally,  it  has  the  appear- 
ance of  a  minute  granule,  sometimes  scarcely  larger  than  a  micro- 
some.  It  is  often  surrounded  by  a  small  area  of  a  granular  or  finely 
reticular  or  radially  striated  cytoplasm,  known  as  the  attraction- 
sphere  or  centrosphere. 

B.  THE  NUCLEUS. 

The  second  constant  element  of  the  cell  is  the  nucleus.  As  a 
rule,  it  is  sharply  defined,  and  in  its  simplest  form  consists  of  a 
round  vesicle  of  a  complicated  structure  composed  of  several  sub- 
stances. The  form  of  the  nucleus  corresponds  in  general  to  the 
shape  of  the  cell ;  in  an  elongated  cell,  it  is  correspondingly  long, 
and  flattened  where  the  cell  is  plate-like  in  shape.  The  nucleus  of 
a  wandering  cell  that  is  in  the  act  of  passing  through  a  narrow  inter- 
cellular cleft  adapts  itself  to  the  changes  of  form  in  the  cell  without 
being  permanently  altered  in  shape.  In  other  words,  the  nucleus  is 
soft,  and  can  be  easily  distorted  by  any  solid  substances  within  or 
without  the  protoplasm,  only  to  resume  its  original  form  when  the 
pressure  is  removed.  It  possesses,  then,  a  certain  amount  of  elas- 
ticity. Movements  of  certain  nuclei,  entirely  independent  of  the  sur- 
rounding protoplasm,  have  often  been  observed.  It  is  only  rarely 
that  the  form  of  the  nucleus  differs  materially  from  that  of  the  cell. 
This,  however,  occurs  in  the  nuclei  of  leucocytes,  which  are  often 
irregular,  and  may  even  be  ring-shaped.  In  certain  arthrozoa, 
branching  forms  of  nuclei  occur,  as  also  in  the  skin  glands  of  turtles. 
The  proportionate  size  of  nucleus  to  cell-body  varies  greatly  in 
different  cells.  Especially  large  nuclei  are  found  in  immature  ova, 
in  certain  epithelial  cells,  etc. 

The  contents  of  the  nucleus  consist  of  a  framework  or  reticu- 
lum,  in  the  meshes  of  which  there  is  found  a  semifluid  substance. 
In  treating  the  nuclei  with  certain  stains,  the  nuclear  reticulum  will 
be  seen  to  consist  of  two  constituents,  a  substance  appearing  in 
the  form  of  variously  shaped,  minute  granules,  which  stains  deeply, 
and  is,  therefore,  known  as  chromatin.  This  is  imbedded  in  and 
deposited  on  a  less  stainable  network,  the  linin.  The  meshes  of  this 
network  are  occupied  by  a  transparent,  semifluid  substance,  which 
does  not  stain  easily,  and  is  known  as  the  achromatic  portion  of  the 
nucleus.  It  is  also  known  as  paralinin,  nuclear  sap,  karyolymph,  or 
nucleoplasm.  Chemically,  chromatin  belongs  to  those  albuminous 
substances  known  as  nucleins. 

In  well-stained  nuclei  of  considerable  size  the  chromatin  gran- 
ules are  seen  closely  placed  in  a  continuous  row  throughout  the  net- 
work of  linin,  which  penetrates  the  nuclei  in  all  directions.  In 


56  THE    CELL. 

every  resting  nucleus  one  or  more  small  round  bodies  are  found 
imbedded  in  the  nucleoplasm.  These  are  known  as  true  nucleoli, 
and  do  not  stain  quite  so  deeply  as  the  chromatin.  The  fact  that 
certain  reagents  dissolve  the  chromatin,  but  not  the  true  nucleoli, 
proves  that  the  substance  of  which  the  latter  are  composed  is  not 
identical  with  chromatin, — and  is,  therefore,  known  as  paranuclein 
(F.  Schwartz). 

In  many  cases  we  find  in  the  linin,  granules  of  a  substance 
known  as  lanthanin,  which  displays  a  marked  affinity  for  the  so- 
called  acid  anilin  stains,  in  contradistinction  to  chromatin,  which 
stains  principally  with  the  basic  anilin  colors.  These  are  known  as 
oxychromatin  granules  in  contradistinction  to  the  basichromatin 
granules  of  the  chromatin  (M.  Heidenhain,  94). 

The  true  nucleoli  should  not  be  confused  with  the  slight  swell- 

o 

ings  of  the  chromatin  network  found  at  the  junction  of  the  threads, 
and  known  as  net-knots,  or  karyosomes. 

Surrounding  the  resting  nucleus  is  usually  a  nuclear  membrane 
resembling  in  many  respects  chromatin.  As  a  rule,  it  does  not  form 
a  continuous  layer,  but  is  perforated,  having  openings  that  contain 
nuclear  fluid.  We  have,  then,  both  substances,  chromatin  and 
nucleoplasm,  as  elements  of  the  nuclear  membrane.  Besides  this, 
the  nuclear  membrane  receives  an  outer  layer,  differentiated  from  the 
protoplasm.  Later  investigations  have  shown  that  even  during  a 
period  of  rest  the  relationship  of  the  nucleus  to  the  protoplasm  of 
the  cell  is  much  more  intimate  than  was  heretofore  believed  (vid. 
B.  Reinke,  94). 

A  resting  nucleus — i.e.,  one  not  in  process  of  division — usually 
consists,  therefore,  of  a  sharply  defined  membrane,  which  has  in  its 
interior  a  chromatic  (nuclein)  and  an  achromatic  (linin)  network,  a 
nuclear  fluid  (paralinin),  and  nucleoli  (paranuclein). 

The  chromatin  of  the  nucleus  is  not  always  in  the  form  of  a  net- 
work. In  some  cases — as,  for  instance,  in  the  premature  ova  of 
certain  animals  (O.  Hertwig,  93.  II)  and  in  spermatozoa — it  is  col- 
lected in  compact  bodies.  In  the  ova  it  may  often  be  mistaken  for 
a  true  nucleolus  (germinal  spot).  In  this  case,  however,  it  consists 
of  nuclein,  and  not  of  paranuclein. 


C  NUCLEAR  AND  CELL-DIVISION* 

The  founders  of  the  cell  theory  believed  in  what  may  be  known 
as  a  modification  of  the  theory  of  spontaneous  generation,  stating  that 
cells  might  originate  from  a  structureless  substance  known  as  kyto- 
blastema  or  blastema,  in  which  a  nucleus  was  formed  by  precipita- 
tion. Henle  (1841)  drew  attention  to  the  fact  that  cells  might  mul- 
tiply by  the  separation  of  small  portions  of  the  cell-body,  a  process 
known  as  budding ;  and  Barry  (1841)  stated  that  during  the  multi- 
plication of  cells  the  nuclei  divided.  The  same  year  Remak 


NUCLEAR    AND    CELL-DIVISION.  5/ 

observed  division  of  cells  in  the  blood  of  embryos.  Goodsir  (1845) 
originated  the  theory  that  all  cells  were  developed  from  preexisting 
cells.  This  was  first  clearly  stated  as  a  general  law  by  Virchow 
(1855),  and  his  saying,  "  Ouinis  cellula  a  cellula]'  is  constantly  being 
verified.  Our  more  accurate  knowledge  of  cell-division  dates,  how- 
ever, from  more  recent  times  (1873—80),  when  Schneider,  Fol,  Stras- 
burger,  Flemming,  and  many  others  demonstrated  that  during  the 
division  of  the  cell  the  nucleus  passed  through  a  series  of  compli- 
cated changes  which  resulted  in  an  exact  division  of  the  chromatin. 
The  phenomena  which  usher  in  cell-division  are  especially 
noticeable  in  the  nucleus,  the  elements  of  which  are  arranged  and 
transformed  in  a  typic  manner.  During  the  division  of  the  nucleus 
the  nuclear  membrane  is  lost,  and  the  relationship  of  the  substances 
of  the  nucleus  to  the  protoplasm  of  the  cell  is  a  very  intimate  one. 
As  a  consequence,  during  the  middle  phases  of  division  there  is  no 
well-defined  demarcation  between  the  nucleus  arid  the  cell-body. 
As  a  rule,  the  mother  cell  and  nucleus  divide  into  two  daughter 
cells,  each  having  a  nucleus,  alike  in  every  particular.  It  was  early 
observed,  however,  that  occasionally  cells  divided  by  a  much  sim- 
pler process,  in  which  case  the  nucleus  did  not  pass  through  such 
complicated  changes.  Accordingly,  two  distinct  types  of  cell- 
division  are  recognized,  which  are  distinguished  as  mitosis,  karyoki- 
nesis,  or  indirect  cell-division,  and  amitosis,  or  direct  cell-division. 
Both  lead  to  the  formation  of  two  nuclei,  which  are  known  as 
daughter  nuclei  as  distinguished  from  the  original  mother  nucleus. 

J.  MITOSIS  OR  KARYOKINESIS  (INDIRECT  CELL-DIVISION). 

The  description  of  the  process  of  mitotic  cell-division  is  compli- 
cated by  the  fact  that  structural  changes  are  observed  which  occur 
simultaneously  in  the  nucleus,  centrosome,  and  cytoplasm.  This 
fact  should  be  borne  in  mind,  as,  for  the  sake  of  clearness,  a  sepa- 
rate description  of  the  changes  involving  each  of  these  structures 
seems  demanded.  The  process  of  mitotic  cell-division  may  be 
divided  into  four  periods  or  phases,  which  follow  one  another  with- 
out clearly  defined  limits  : 

The  prophases,  in  which  the  nuclear  membrane  disappears,  the 
chromatin  is  transformed  into  definite  threads,  and  the  centrosome 
and  centrosphere  undergo  important  changes.  This  is  the  prepar- 
atory stage. 

The  metaphases,  in  which  the  division  and  the  separation  of  the 
chromatin  take  place. 

The  anaphases,  in  which  the  daughter  nuclei  are  formed  and  the 
cell-protoplasm  begins  to  divide. 

The  telophases,  in  which  the  division  of  the  cell  is  completed. 

To  give  a  better  understanding  of  this  process,  we  have  inserted 
a  series  of  diagrammatic  figures  (9-19),  giving  the  cells  the  shape 
of  an  ellipsoid.  We  can  then  distinguish  a  long  axis,  two  polar 


THE    CELL. 


Crown  of 
chromo- 


Crown  of 
chromo- 


Fig.  ii. 


Fig.  12. 


Fig.  13.  Fig.  14. 

Figs.  9-14. — Diagrammatic  representation  of  the  processes  of  mitotic  cell-  and  nuclear 

division. 

Figs.   9-12,  Prophases  ;  Figs.    13,  14,  metaphases. 

Fig.  9,  Resting  nucleus;  Fig.  10,  coarse  skein  or  spirem  ;  Fig.  1 1,  fine  skein  or 
spirem ;  Fig.  12,  segmentation  of  the  spirem  into  single  chromosomes;  Fig.  13,  longi- 
tudinal division  of  the  chromosomes ;  Fig.  14,  bipolar  arrangement  of  the  separated 
chromosomes. 


NUCLEAR    AND    CELL-DIVISION. 


59 


Uniting 
filaments. 


Fig-  15- 


Fig.  16. 


ooo    o--— =s^T^ Cell-plates. 


Chromo- 
somes. 


Fig.  17. 


Fig.  18. 


A Nucleolus. 


Fig.  19. 

Figs.  15-19. — Diagrammatic  representation  of  the  processes  of  mitotic  cell-  and  nuclear 

division. 

Figs.    15-18,  Anaphases;  Fig.  19,  telophases. 

Fig.  15,  wandering  of  the  chromosomes  toward  the  poles;  Fig.  1 6,  diaster;  Figs. 
17  and  18,  formation  of  the  dispirem;  Fig.  19,  two  daughter  cells  with  resting  nuclei. 
To  simplify  the  figures  12-17,  we  have  sketched  in  only  a  few  chromosomes.  In  Fig. 
1 6  it  is  seen  that  the  cell-body  is  also  beginning  to  divide. 


6o 


THE    CELL. 


Fig.  20. 


Fig.  21. 


Fig.  22. 


HI 

xiixj^lii^^ 


Fig.  23.  Fig.  24. 

Figs.  20-24. — Mitotic  cell-division  of  fertilized  whitefish  eggs — Coregonus  albus. 
Fig.  20,  Cell  with  resting  nucleus,  centrosome,  and  centrosphere  to  the  right  of  the 
nucleus;    Fig.   21,  cell  with   two  centrospheres ,  with  polar  rays  at  opposite  poles  of 
nucleus ;  Fig.  22,  spirera ;  Fig.  23,  monaster ;  Fig.  24,  metakinesis  stage. 


regions  corresponding  to  the  ends  of  the  axis,  and  an  equatorial 
plane.  The  latter  is  horizontal  to  the  axis,  equally  distant  from 
both  poles,  and  passes  through  the  middle  of  the  nucleus.  The 
division  of  the  cell  takes  place  in  this  plane.  A  series  of  figures 
(20-27),  showing  the  different  phases  of  mitotic  cell-division  of  the 
fertilized  eggs  of  the  whitefish  (Coregonus  albus),  is  given  ;  the 
changes  involving  the  centrosome,  centrosphere,  and  cytoplasm  are 
clearly  illustrated.  Figure  28,  showing  a  small  portion  of  a  sec- 
tion through  the  testis  of  the  salamander,  the  object  in  which  Flem- 
ming  first  observed  this  complicated  series  of  changes,  presents  the 
appearance  more  generally  seen  during  mitotic  cell-division  of  the 
tissue  cells  of  the  higher  vertebrates. 

(a)  Prophases. — The  changes  occurring  in  the  nucleus  will 
be  considered  first.  At  the  beginning  of  the  process  of  mitosis,  the 
chromatin  network,  consisting  of  chromatin  granules^s  transformed 
into  a  twisted  skein  of  threads,  beginning  at  the  periphery  of  the 


NUCLEAR    AND    CELL-DIVISION. 


61 


Fig.  25. 


Fig.  26. 


Fig.  27. 

Figs.  25-27. — Mitotic  cell-division  of  fertilized  whitefish  eggs — Coregonus  albus. 
Fig.   25,  Metakinesis  stage  ;  Fig.   26,  diaster  ;  Fig.  27,  late  stage  of  dispirem,  the 
cell-protoplasm  almost  divided. 


nucleus.  This  skein  of  threads  is  known  as  the  spirem  or  mother 
skein,  and  may  appear  as  a  single  thread,  which  breaks  up  into  a 
definite  number  of  segments,  or  the  segments  may  appear  as  such 
when  the  skein  is  forming.  At  first  the  threads  are  coarse  and  often 
somewhat  irregular,  staining  much  more  deeply  than  the  linin 
network.  The  separate  segments  of  chromatin  are  known  as 
chromosomes  (Waldeyer,  88).  They  appear,  as  a  rule,  in  the  form 
of  rods  varying  in  length  and  thickness,  and  staining  very  deeply, 
and  often  bent  into  characteristic  U-shaped  loops.  The  bent  portion 
of  each  loop  is  called  its  crown.  "  Every  species  of  plant  or  ani- 
mal has  a  fixed  and  characteristic  number  of  chromosomes,  which 
regularly  recurs  in  the  division  of  all  its  cells  ;  and  in  all  forms 
arising  by  sexual  reproduction  the  number  is  even"  (Wilson,  96). 
In  man  the  number  of  chromosomes  is  given  as  sixteen  by  Barde- 
leben  (92)  and  Wilson  (96),  and  as  twenty-four  by  Flemming  (98). 
During  the  formation  of  the  spirem  the  nuclear  membrane,  as  a 
rule,  disappears.  The  nucleolus  is  also  lost  sight  of,  although  the 
manner  of  its  Disappearance  can  not  be  definitely  stated.  The  net- 
knots  are  no  doubt  taken  up  by  the  chromosomes.  The  chromo- 


62  THE    CELL. 

somes  are  now  free  in  the  protoplasm  ;  gradually  the  crown  of  each 
chromosome  approaches  the  center  of  the  space  occupied  by  the 
nucleus,  and  the  chromosomes  form  a  characteristic,  radially 
arranged  stellate  figure,  known  as  the  monaster,  in  the  equatorial 
plane  of  the  cell.  During  the  progress  of  the  changes  affecting  the 
chromatin  of  the  nucleus  and  resulting  in  the  formation  of  the 
chromosomes,  important  phenomena  are  observed,  connected  partly 
with  the  achromatic  substance  of  the  nucleus,  more  especially  with 
the  centrosome,  centrosphere,  and  cytoplasm  of  the  cell.  These 
phenomena  result  in  the  formation  of  a  complicated  structure  known 
as  the  achromatic  spindle  or  amphiaster.  Its  development  is  as  fol- 
lows :  The  centrosome  and  centrosphere,  as  has  been  stated,  usu- 
ally lie  in  the  protoplasm  to  one  side  of  the  nucleus.  If,  at  the  be- 
ginning of  the  division,  the  centrosome  be  single,  it  divides,  and  the 
two  centrosomes  begin  to  separate,  causing  a  division  of  the  centro- 
sphere. Between  the  centrosomes  are  usually  seen  finely  drawn-out 
connecting  threads.  The  centrosomes,  each  of  which  is  surrounded 
by  a  centrosphere,  now  move  apart,  and  a  structure  known  as  the 
central  spindle,  and  consisting  of  fine  threads  arranged  in  the  form 
of  a  spindle,  develops  between  them.  At  each  end  of  the  central 
spindle  is  found  a  centrosome  surrounded  by  a  centrosphere  from 
which  radiate  into  the  cytoplasm  fine  fibers  known  as  polar  rays. 
During  the  formation  of  the  achromatic  spindle  the  nuclear  mem- 
brane disappears  and  the  chromosomes  develop,  as  above  described. 
Some  fibers,  which  seem  to  have  their  origin  from  the  centrosphere, 
grow  into  the  spirem  formed  of  chromosomes,  which  they  appear  to 
pull  into  the  equatorial  plane  of  the  cell,  which  is  also  the  equator 
of  the  central  spindle.  Thus,  the  nuclear  figure  above  described 
as  the  monaster  is  formed.  In  other  cases  the  centrosomes 
and  centrospheres  continue  moving  apart  until  opposite  each  other 
and  separated  by  the  nucleus  (Figs.  21,  22).  As  the  nuclear 
membrane  disappears  and  the  spirems  and  chromosomes  are  form- 
ing, the  central  spindle  develops,  its  fibers  running  from  centro- 
sphere to  centrosphere.  The  polar  rays  also  develop  in  the  cyto- 
plasm at  the  same  time.  As  the  central  spindle  develops,  the 
chromosomes  arrange  themselves  or  are  arranged  about  its  equator 
— monaster. 

(b)  Metaphases. — Usually,  during  the  formation  of  the  monaster, 
or  immediately  after  its  formation  (sometimes  in  the  spirem  stage  or 
even  earlier),  the  most  important  process  of  cell -division  takes 
place.  Each  chromosome  divides  longitudinally  into  two  daughter 
chromosomes.  The  loops  first  divide  at  the  crown,  the  cleft  extend- 
ing up  either  limb  until  the  free  ends  are  reached.  The  smallest 
particle  of  chromatin  divides,  retaining  the  exact  relative  position  in 
the  twin  chromosomes  that  it  possessed  in  the  mother  chromo- 
some. The  daughter  chromosomes  now  wander  over  the  central 
spindle,  their  crowns  presenting,  in  opposite  directions  toward  the 
poles  of  the  cell.  This  process  is  known  as  metakinesis.  Two  stel- 


NUCLEAR    AND   CELL-DIVISION.  63 

late  figures  are  developed  about  the  respective  poles  of  the  central 
spindle.  The  appearance  presented  is  known  as  a  diaster.  Our 
knowledge  of  the  part  taken  by  the  amphiaster  or  achromatic 
spindle  in  metakinesis  is  not  above  controversy.  It  would  appear, 
however,  that  certain  cytoplastic  fibers,  which  arise  from  the  cen- 
trosphere  and  hang  over  the  central  spindle  and  chromosomes, 
designated  as  mantle  fibers,  assist  in  drawing  the  daughter  chromo- 
somes toward  the  poles  of  the  central  spindle. 

(c)  Anaphases. — After  the  formation  of  the  diaster,  the  loops  be- 
longing to  each  stellate  figure  are  joined  together  to  form  a  skein, 
thus  forming  the  dispirem.  The  chromatin  threads  of  the  two 
skeins  gradually  assume  the  disposition  found  in  the  resting  nucleus. 
This  process  takes  place  in  such  a  way  that  the  threads  of  the 

Dispirem. 


Diaster. 


Diaster. 


Monaster. 


Resting  nucleus. 

Metakinesis. 

—  Diaster. 


.-  Daughter  cells. 


Spirem. 
Fig.  28. — Mitotic  division  of  cells  in  testis  of  salamander  (Benda  and  Guenther). 


skeins  (or  the  single  thread)  send  out  lateral  processes.  These 
interlace,  and  little  by  little  reproduce  the  network  of  the  resting 
nucleus  ;  at  the  same  time  the  nuclear  membrane  and  the  nucleolus 
reappear.  In  this  stage  the  changes  that  lead  to  the  division  of  the 
cell-body  are  observed.  In  some  cases  the  division  of  the  cell-body 
is  ushered  in  by  an  equatorial  differentiation  of  the  connecting 
threads  of  the  central  spindle.  Chains  of  granules,  arranged  in 
double  rows,  are  seen  to  appear  in  this  region.  The  cell  now  begins 
to  contract  at  its  equator,  the  contraction  extending  between  the 
two  chains  of  granules  until  the  cell  is  completely  divided.  At 
this  time,  also,  the  threads  of  the  amphiaster  disappear  or  are  drawn 
into  the  nucleus.  The  centrosomes,  with  centrospheres,  again  lie 
by  the  side  of  the  daughter  nuclei. 


64  THE    CELL. 

According  to  the  opinion  of  C.  Rabl  (85),  there  remains  in  the 
nucleus,  even  after  it  has  fully  returned  to  a  state  of  rest,  a  polar 
arrangement  of  the  chromatin  loops — that  is,  an  arrangement  of  the 
axis  of  the  loops  in  the  direction  of  the  centrosphere.  The  area 
toward  which  the  crowns  of  the  loops  point  is  known  as  the  polar 
field. 

The  equatorial  differentiation  of  the  connecting  threads  of  the 
central  spindle,  above  mentioned,  was  first  observed  in  vegetable 
tissue,  and  is  known  as  the  cell-plate.  (Fig.  27.)  In  animal  cells  such 
a  plate  is  relatively  rare,  and,  when  seen,  is  found  developed  in  a 
rudimentary  form  (v.  Kostanecki  92,  I). 

(d}  Telophases  (M.  Heidenhain  94). — In  these  phases  of  mitosis 
the  cell  divides  completely.  The  daughter  nuclei  and  centrospheres, 
which  do  not  yet  occupy  their  normal  position  in  the  daughter  cells, 
show  movements  that  result  in  their  assuming  their  normal  positions. 

From  our  description  it  is  seen  that  the  anaphases  represent  the 
same  stages  as  the  prophases,  only  in  an  inverted  sequence.  In  the 
latter  case,  the  result  is  the  resting  nucleus,  while  the  prophases  lead 
to  the  metaphases. 

The  fertilized  ovum  also  divides  by  indirect  nuclear  division. 
(Figs.  20-27.)  From  it  are  derived,  by  this  process,  the  seg- 
mentation cells,  or  blastonieres,  from  which  the  whole  embryo  is 
developed. 

(e)  The  Heterotypic  Form  of  Mitosis. — The  above-described 
type  of  indirect  or  mitotic  nuclear  division  (Jwuicotypic  mitosis)  is 
the  usual  one.  Variations,  however,  occur,  as,  for  instance,  in  the 
so-called  lieterotypic  form  of  division  (Flemming  87),  which  occurs 
in  certain  cells  of  the  testes  (spermatocytes).  In  this  form  the  first 
stages  are  lacking,  the  nucleus  possessing  from  the  beginning  a 
skein -like  structure.  The  longitudinal  splitting  and  division  of  the 
chromatin  threads  take  place  during  the  first  spirem  stage,  after  which 
there  is  a  phase  in  which  the  figure  may  be  compared  with  an  aster 
of  ordinary  mitosis,  although  the  free  ends  of  the  threads  in  this 
case  are  seldom  observed.  The  latter  is  due  to  the  fact  that  after 
the  longitudinal  splitting,  the  ends  of  the  chromosomes  remain 
united,  or,  if  entire  separation  occurs,  they  are  again  joined.  In  this 
way  closed  loops  are  formed  extending  from  pole  to  pole.  Later 
the  threads  break  at  the  equator  and  move  toward  the  poles,  again 
dividing  to  form  the  daughter  stars. 


2.  AMITOSIS. 

Very  different  from  the  indirect  form  of  nuclear  division  is  the 
direct  or  amitotic.  It  appears  to  occur  seldom  as  a  normal  process, 
and  is  only  exceptionally  followed  by  a  subsequent  cell-division 
(vid.  Flemming,  91,  III).  As  a  consequence,  this  process,  in  most 
cases,  results  in  the  formation  of  polynuclear  cells  (polynu  clear  leu- 
cocytes, giant-cells,  etc.).  The  complicated  nuclear  figures  of 


PROCESS    OF   FERTILIZATION.  65 

indirect  division  are  here  entirely  absent.  The  nucleus  merely  con- 
tracts at  a  certain  point  and  separates  into  two  or  more  fragments 
(direct  fragmentation,  Arnold)  ;  often  the  nucleus  first  assumes  an 
annular  form  and  then  breaks  up  into  several  fragments,  which 
remain  loosely  connected  (polynuclear  cells).  Centrospheres  are 
also  present,  and  appear  to  take  a  prominent  part  in  the  whole  pro- 
cess, although  the  exact  relationship  between  the  achromatiri  and 
chromatin  has  not  as  yet  been  determined. 

Arnold  (83)  gives  the  following  comparison  of  indirect  and  direct 
nuclear  division  :  (i)  Segmentation.  Division  of  the  nuclei  in  the  equa- 
torial plane  into  two  or  more  equal  parts ;  (#  )  direct  segmentation 
without,  (b)  indirect  segmention  with,  increase  and  changed  arrangement 
of  the  chromatic  substance  (mitosis).  (2)  Fragmentation.  Contraction 
of  the  nucleus  at  some  point,  forming  two  or  more  equal,  but  oftener  un- 
equal, nuclear  fragments;  (c)  direct  fragmentation  without,  (d)  indirect 
fragmentation  with,  increase  and  changed  arrangement  of  the  chromatic 
substance. 


D.  PROCESS  OF  FERTILIZATION. 

The  sexual  cells  form  a  special  group  among  cells  in  general. 
Before  the  division  of  the  egg-cell  leading  to  the  development  of 
the  embryo  can  take  place,  the  ovum  must  be  impregnated  (the  so- 
called  parthenogenetic  ova  are  an  exception  to  this  rule).  Fertili- 
zation is  produced  by  the  male  sexual  cell,  the  spermatozoon. 

The  process  of  fertilization  consists  in  a  conjugation  of  two  sex- 
ual cells,  and  in  this  process  certain  peculiarities  in  the  behavior  of 
both  cells  must  be  mentioned. 

The  cell  forming  the  ovum  and  the  one  forming  the  spermato- 
zoon must  pass  through  certain  stages  before  fertilization  can  be 
accomplished.  These  consist  in  the  loss  of  half  their  chromosomes 
by  the  nuclei  of  both  sexual  cells.  In  this  way  are  produced  the 
matured  sexual  cells  (ova  and  spermatozoa),  which  retain  only 
half  of  the  number  of  chromosomes  of  a  somatic  (body-)  cell. 
In  the  conjugation  of  the  male  and  female  sexual  cells  their  nuclei 
unite  to  form  a  single  nucleus,  known  as  the  segmentation  nucleus. 
Consequently,  this  nucleus  contains  the  same  number  of  chromo- 
somes as  does  that  of  a  somatic  cell. 

In  its  earlier  developmental  stages  the  ovum  is  an  indifferent  cell, 
the  nucleus  of  which  is  known  as  the  germinal  vesicle.  As  the 
ovum  matures  the  germinal  vesicle  approaches  the  periphery,  and  a 
peculiar  metamorphosis,  which  may  be  regarded  as  a  double,  un- 
equal division  of  the  egg-cell,  takes  place.  One  portion,  in  the  case 
of  both  divisions,  is  much  smaller  than  the  other",  and  is  known  as 
a  polar  body.  At  the  close  of  these  divisions,  during  which  the 
chromosomes  have  been  reduced  to  half  the  original  number,  there 
are,  therefore,  two  polar  bodies  and  the  matured  ovum,  which  is 
now  ready  for  impregnation. 
5 


66 


THE    CELL. 


Membrane  of 
ovum. 

Nucleus  of 

ovum. 
Spermatozoon 

entering. 


Protoplasm  of 
ovum  with 
deutoplastic 
granules. 


Fig.  29. 


Female 
pronu- 
cleus. 


—   Male 
ill  pronu- 

cleus. 


Fig. 


Fig-  31- 


Figs.   29-31. — Diagrams  of  the  process  of  fertilization,  after  Boveri  (88). 
Figure  29,  the  ovum  is  surrounded  by  spermatozoa,  one  of  which  is  in  the  act  of 
penetration.     Toward  it  the  yolk  is  pushed  forward  in  a  short,  rounded  process.      Figure 
30,  the  tail  of  the  spermatozoon  has  disappeared.     Beside  the  head  is  a  centrosome  with 
polar  radiation.     Figure  31,  the  pronuclei  approach  each  other. 


The  development  of  the  male  sexual  cell  in  its  earlier  stages  is  sim- 
ilar to  that  of  the  ovum.  They  are  derived  from  cells  known  as  sper- 
matogones.  These  divide  into  equal  parts,  forming  the  cells  of  a 
second  generation,  the  spermatocytes.  From  a  further  division  of  the 
spermatocytes,  during  which  division  the  chromosomes  are  reduced 
to  half  the  number,  the  spennatids  are  produced.  These  latter  are 
then  changed  directly  into  spermatozoa.  The  reduction  division  of 
the  egg-cell  and  that  of  the  spermatocytes  is  in  principle  the  same, 
except  that  in  spermatogenesis  all  cells  become  matured  sexual  cells 
(spermatozoa).  In  short,  there  is  here  an  absence  of  structures 
analogous  to  the  polar  bodies,  which  degenerate  after  maturation 
of  the  ovum. 

The  spermatozoa  are  flagellate  cells.  The  head  consists  prin- 
cipally of  nuclear  substance,  to  which  is  added  a  smaller  middle- 
piece  containing,  according  to  the  investigations  of  Pick,  the  centro- 
some. These  two  portions  of  the  male  sexual  cell,  the  head-  and 


PROCESS    OF   FERTILIZATION. 


67 


Tt&f* —  Centrosome. 


Male  pronu- 
cleus. 


Female  pro- 
nucleus. 


Chromo- 
somes of 
male  pro- 
nucleus. 

Centrosome. 


Fig.  32- 


Fig.  33- 


Chromosomes 
from  egg-nu- 
cleus. 


from  sperm- 
nucleus  (male 
pronucleus). 


—  Centrosome. 


Fig.  34- 

Figs.   32-34. — Diagrams  of  the  process  of  fertilization,  after  Boveri  (88). 
Figure  32,  from  the  spirems  in  the  pronuclei,  chromosomes  have  been  formed.     The 
centrosphere  has  divided.    Figure  33,  the  double  chromosomes  of  the  two  pronuclei  lie  in 
the  equatorial  plane  of  the  ovum.      Figure  34,  the  ovum  has  divided.     Chromosomes 
from  the  male  and  female  elements  are  seen  in  equal  numbers  in  both  daughter  nuclei. 


middle -piece,  are  the  most  important,  and  are  exclusively  con- 
cerned in  fertilization,  the  flagellum  or  tail  playing  no  part  in  this 
process. 

The  spermatozoon  usually  penetrates  the  ovum  after  the  first 
polar  body  has  been  extruded.  The  tail  disappears  during  this 
process,  being  either  left  at  the  periphery  of  the  egg  or  dissolved  in 
the  protoplasm.  From  this  time  the  head  represents  the  so-called 
male  pronucleus,  and  the  middle-piece  the  Centrosome.  From  this 
stage  the  male  pronuclens  undergoes  changes,  the  first  of  which 
consists  of  a  loosening  of  the  chromatin.  Chromatin  granules  are 
formed,  which  later  arrange  themselves  in  the  form  of  chromo- 
somes. 

After  the  second  polar  body  has  been  extruded,  the  chro- 
matin remaining  in  the  ovum  is  transformed  into  the  female  pro- 
nucleus.  The  latter  then  approaches  the  male  pronucleus,  the 
membranes  of  both  nuclei  disappearing.  The  chromosomes  of 


68  THE    CELL. 

the  two  nuclei  thus  formed  are  of  equal  number,  and  now  come  to 
lie  together.  After  a  longitudinal  division  of  the  chromosomes, 
the  daughter  chromosomes  glide  along  the  filaments  of  the  achro- 
matic spindle,  developed  from  the  centrosome  of  the  male  pronu- 
cleus,  toward  its  two  poles,  as  in  ordinary  mitosis.  This  they  do 
in  such  a  manner  that  an  equal  distribution  of  the  male  and  female 
daughter  chromosomes  results.  Then  follow  the  stages  of  the  ana- 
phase. 

From  the  above  description  of  the  process  of  fertilization  it  is 
seen  that  it  consists,  in  the  end,  of  a  union  of  the  nuclei  of  both 
sexual  cells. 

If  paternal  qualities  are  inherited  by  the  offspring,  this  can  only 
take  place  through  the  nucleus,  or  through  the  centrosome  of  the 
male  sexual  cell.  In  other  words,  it  can  be  safely  said  that  these 
structures,  or  the  nucleus  alone,  are  the  principal  means  of  trans- 
mitting inherited  qualities.  The  same  may  also  be  said  of  the 
female  pronucleus.  There  is  no  doubt  that  the  first  two  seg- 
mentation cells  of  the  ovum  are  equally  provided  with  male  and 
female  nuclear  elements.  Since  all  future  cells  are  derivatives  of 
these  two,  it  is  possible  that  the  nucleus  of  every  somatic  cell 
(body-cell)  is  hermaphroditic. 


E.  CHROMATOLYSIS. 

In  the  living  organism  many  cells  are  destroyed  during  the 
various  physiologic  processes  and  replaced  by  new  ones.  On  the 
death  of  a  cell,  changes  take  place  in  its  nucleus  which  result  in  its 
gradual  disappearance.  These  processes,  which  seem  to  follow 
certain  definite  but  as  yet  unfamiliar  laws,  have  been  known  since 
their  study  by  Flemming  (85,  I)  by  the  name  of  chromatolysis 
(karyolysis).  The  nuclei  during  the  course  of  these  changes  show 
many  varied  pictures. 

TECHNIC 

113.  In  a  fresh  condition,  cells  do  not  show  much  of  their  internal 
structure.  Epithelial  cells  of  the  oral  cavity,  which  can  easily  be  ob- 
tained and  examined  in  the  saliva,  show  really  nothing  except  the  cell 
outlines  and  the  nuclei.  More,  however,  can  be  seen  in  young  ova  iso- 
lated from  the  Graafian  follicles  of  mammalia  ;  or  the  examination  may  be 
facilitated  by  using  the  ovary  of  a  young  frog.  Tissues  that  are  especially 
adapted  for  the  observation  of  cells  in  a  fresh  condition  are  small  ova, 
blood-corpuscles,  and  epithelia  of  certain  invertebrate  animals  (shellfish, 
etc.).  Unicellular  organisms  such  as  amebae,  infusoria,  and  many  low 
forms  of  vegetable  life  make  also  good  material  for  this  purpose. 

Protoplasmic  currents  are  best  seen  in  the  tactile  hairs  of  the  net- 
tle. Should  fresh  animal  cells  be  desired,  amebse  can  occasionally  be 
found  in  muddy  or  marshy  water.  The  same  phenomena  may  be  ob- 
served in  the  leucocytes  of  the  frog  or,  better  still,  in  the  blood  of  the 
crab. 


CHROMATOLYSIS.  69 

114.  In  order  to  make  a  detailed  study  of  the  minute  relationship 
of  the  different  cellular  structures,   it  is   necessary  to  fix  the  cells ;  the 
same  is  true  of  nuclear  division  and  cell  proliferation.     Although  this 
process  has  been  observed  in  living  cells,  it  was  not  until  it  had  been 
thoroughly  worked  out  in  preserved  preparations.     The  best  results  in  the 
study   of  the    cell  are   obtained  by  methods   that  will  be  subsequently 
described.      Fresh  tissues  are  absolutely  essential. 

According  to  Hammer,  mitosis  in  man  does  not  cease  immediately 
after  death.  The  nuclei  suffer  chromatolytic  destruction,  and  the  achro- 
matic spindle  is  the  last  element  to  disappear. 

115.  Flemming's  solution  (yid.  T.  17)  here  deserves  first  men- 
tion as  a  fixative.     The  tissues  are  imbedded,  sectioned,  and  stained 
with   safranin   (vid.   T.    66).      An   equally  good  fixative  is  Hermann's 
solution,  which  may  be  combined  with  a  subsequent  treatment  with  pyro- 
ligneous  acid  (vid.  T.  18).      Rabl  fixes  with  a  0.1-0.12%   solution  of 
chlorid  of  platinum,  washes  with  water,  passes  into  gradually  stronger 
alcohols,  then   stains  with   Delafield's  hematoxylin    (vid.   T.   62),  and 
finally  examines  the  preparation  in  methyl  alcohol. 

116.  Mitoses  can  also  be  seen  by  fixing  in  corrosive  sublimate, 
picric  acid,  chromic  acid,  etc.,  and  staining  in  bulk  with  hematoxylin 
or  carmin,  although  perhaps  not  so  well  as  by  the  preceding  method. 
The  objects  to  be  examined  are  best  when  obtained  from  young  and  grow- 
ing animals,  especially  those  possessing  large  cells.     Above  all  are  to  be 
recommended  the  larvae  of  amphibia,  like   the   frog,   triton,  and  sala- 
mander.      If  examination  by  means   of  sections  be    undesirable,    thin 
structures  should  be  procured,  such  as  the  mesentery,  alveoli  of  the  lungs, 
epithelium  of  the  pharynx,  urinary  bladder,  etc.     These  have  the  advan- 
tage of  enabling  one  to  observe  the  whole  cell  instead  of  parts  or  frag- 
ments of  cellular  structures.      In  sections  of  a  larva  that  has  been  fixed  in 
toto,  mitotic  figures  can  be  seen  in  almost  all  the  organs,  and  are  particu- 
larly numerous  in  the  epithelium  of  the  epidermis,  gills,  central  canal  of 
the  brain  and  spinal  cord,  etc.      Other  organs,  such  as  the  blood,  liver, 
and  muscle,  also  show  mitoses. 

117.  Certain  vegetable  cells  are  peculiarly  adapted  to  the  study  of 
mitosis,  as,  for  instance,  those  in  the  ends  of  young  roots  of  the  onion. 
The  onion  should  be  placed  in  a  hyacinth  glass  filled  with  water  and  kept 
in  a  warm  place.     After  two  or  three  days  numbers  of  small  roots  will 
be  found  to  have  developed.      Beginning  at  the  points,   pieces  5  milli- 
meters in  length  are  cut,  which  are  treated  in  the  same  manner  as  animal 
tissues.     These  are  then  cut,  either  transversely  or  longitudinally,  into 
very  thin  sections  (not  over  5  /.*  in  thickness).      In  one  plane,  polar  views 
of  the  mitoses  are  obtained  ;   in  the  other,  lateral  views. 

118.  The  methods  used  for  demonstrating  the  remaining  parts  of  the 
cell  and  its  nucleus  (except  the  chromatin)  are,  as  a  rule,  more  compli- 
cated, and  consequently  less  reliable.      In  order  to  see  the  centrosome, 
the   spindle   fibrils,   the  linin  threads,  and  the  polar  rays,  one  of  the 
methods  already  described  may  be  used  ;  viz.,  the  treatment  with  pyro- 
ligneous  acid  of  objects  previously  fixed  in  osmic  acid  mixtures. 

119.  According  to  Hermann  (93,  II),  sections  from  such  preparations 
can  be  double=stained  as  well  as  those  that  have  not  been  treated  with 
pyroligneous  acid.     They  are  accordingly  stained  with  safranin  in  the 
usual  manner,   and   afterward  treated  from  three  to   five  minutes  with 


/O  THE    CELL. 

the  following  solution  of  gentian  violet  :  5  c.c.  of  a  saturated  alco- 
holic solution  of  the  stain  is  dissolved  in  100  c.c.  of  anilin  water. 
The  latter  is  composed  of  4  c.c.  of  anilin  oil  in  100  c.c.  of  distilled 
water.  This  is  shaken  in  a  test-tube  and  then  filtered  through  a  wet 
filter.  The  sections  are  then  placed  in  a  solution  of  iodin  and  iodid  of 
potassium  (iodin  i  gm.,  iodid  of  potassium  2  gm.,  water  300  c.c.) 
until  they  have  become  entirely  black,  after  which  they  are  immersed  in 
alcohol  until  they  receive  a  violet  tinge  with  a  slight  dash  of  brown.  By 
this  means  the  chromatin  network,  the  resting  nuclei,  and  the  chromo- 
somes in  both  of  the  spirem  stages  appear  bluish -violet,  while  the  true 
nucleoli  are  pink.  The  chromosomes  of  the  aster  and  diaster  are  col- 
ored red. 

120.  Flemming  (91,  III)  recommends  the  following  method  :  Fixation 
by  his  mixture  (T.  17)  ;  the  specimens  or  thin  sections  are  then  placed 
in  safranin  from  two  to  six  days  (T.  66),  washed  for  a  short  time  in 
distilled  water,  and  then  immersed  in  absolute  alcohol  weakly  acidulated 
with  hydrochloric  acid  (i  :  1000),  until  no  more  color  is  given  off.     They 
are  then  washed  again  with  distilled  water  and  placed  in  a  concentrated 
solution  of  anilin -water-gentian -violet  from  one  to  three  hours.     After  a 
third  rinsing  in  distilled  water,  they  come  into  a  concentrated  aqueous 
solution  of  orange  G,  until  they  begin  to  assume  a  violet  color.     Then 
wash  with  absolute  alcohol,  clear  in  clove  or  bergamot  oil,  and  mount  in 
Canada  balsam. 

121.  A  comparatively  simple  method  showing  the  different  structures 
of  the  cell  and  its  nucleus  with  great  clearness  consists  in  staining  with 
Heidenhain's  hematoxylin  (vid.  T.  65). 

122.  Solger  (89,  I  and  91)  has  discovered  that  both  chromosomes 
and  polar  rays  are  shown  in  an  exquisite  manner  in  the  pigment  cells  of 
the  skin  (corium)  of  the  frontal  and  ethmoidal  regions  of  the  common 
pike  (vid.  Fig.  35).     The  preliminary  treatment  is  optional,  Flemming's 
solution  or  corrosive  sublimate  being  the  best.     These  cells  illustrate  the 
stability  of  the  radiate  structures  of  protoplasm,  the  polar  rays  showing 
as  parallel  rows  of  pigment  granules. 

123.  The  various  structures  of  resting  and  dividing  nuclei  and  cells 
are  of  such  a  complicated  nature  that  they  can  be  observed  only  with 
great  difficulty  in  ordinary  objects,  because  of  the  crowding  of  so  many 
elements  into  a  comparatively  small  space.      For  example,  salamandra 
maculosa,   which   has   become   a  classic  histologic  object    through    the 
researches  of  Flemming,  possesses  somatic  cells  whose  nuclei  have  no  less 
than  twenty-four  chromosomes.      (It  may  here  be  remarked  that,  curiously 
enough,  salamandra  atra  has  only  half  this  number. )     Consequently,  van 
Beneden's  discovery  (83),  that  the  somatic  cells  of  ascaris  megalocephala 
have  only  four  primary  chromosomes,  is  a  fact  of  considerable  import- 
ance.    Boveri  (87,  II  and  88)  has  even  found  an  ascaris  showing  only 
two  chromosomes.     As  these  animals  also  show  distinct  achromatic  fig- 
ures in  the  protoplasm  of  their  ova  and  sperm  cells,  they  are  certainly 
worthy  of  being  regarded  as  typic  specimens  for  laboratory   purposes. 
The  processes  of  cell -proliferation  are  almost  diagrammatic  in  their  dis- 
tinctness. 

After  opening  the  abdominal  wall  of  the  animal,  the  ovisacs  are 
removed,  their  numerous  convolutions  separated  as  much  as  possible, 
and  then  fixed  for  twenty-four  hours  in  a  picric-acetic  acid  solution 


CHROMATOLYSIS.  7 1 

(a  concentrated  aqueous  solution  of  picric  acid  diluted  with  2  vols. 
of  water  to  which  i  per  cent,  glacial  acetic  acid  is  added).  Then  fol- 
lows washing  for  twenty-four  hours  with  water,  after  which  the  specimen 
is  transferred  to  increasing  strengths  of  alcohol  (Boveri,  ibid.).  Differ- 
ent regions  of  the  ovisacs  contain  ova  in  various  stages  of  development, 
those  nearest  the  head  containing  cells  ripe  and  ready  for  fecundation, 
while  in  the  more  posterior  regions  are  ova  in  varying  stages  of  segmen- 
tation showing  mitoses.  Specimens  fixed  in  the  manner  above  described 
can  be  stained  with  a  borax-carmin  solution.  After  staining,  the  ova  are 
gently  pressed  out  with  needles  upon  a  slide,  separated,  covered  with  a 
cover- glass,  and  cleared  by  gradual  irrigation  with  glycerin.  The  ova, 
especially  the  segmentation  spheres,  are  very  small,  and  can  be  examined 
only  under  high  magnification.  In  spite  of  the  minuteness  of  the  ob- 
ject and  the  fact  that  the  yolk  does  not  take  the  stain,  and,  on  account  of 


Fig-  35- — Pigment  cell  from  the  skin  of  the  head  of  a  pike  ;   X  650.     T.  No.  122. 


its  high  refractive  index,  distorts  the  picture  to  a  considerable  extent,  the 
mitotic  figures  are  beautifully  distinct. 

124.  Certain  methods  of  treatment  bring  out  in  both  cells  and  nuclei 
the  presence  of  peculiar  granules.  The  latter  have  been  especially 
studied  and  described  by  v.  Altmann  (94,  2d  ed. ).  The  methods  that 
he  applies  are  as  follows :  The  specimens  of  organs  of  recently  killed 
animals  are  fixed  in  a  mixture  consisting  of  equal  volumes  of  a  5% 
aqueous  solution  of  potassium  bichromate  and  a  2%  solution  of  osmic 
acid,  remaining  in  the  mixture  for  twenty-four  hours.  They  are  then 
washed  for  several  hours  in  water  and  treated  with  ascending  strengths 
of  alcohol ;  viz.,  70,  90,  and  100%.  The  specimens  are  now  placed  in 
a  solution  of  3  parts  of  xylol  and  i  part  of  absolute  alcohol,  then  in 
pure  xylol,  and  finally  in  paraffin.  The  tissues  imbedded  in  paraffin 
must  not  be  cut  thicker  than  i  to  2  /a. 

Altmann  mounts  according  to  the  following  method  :    A  rather  thick 


72  THE    CELL. 

solution  of  caoutchouc  in  chloroform  (the  so-called  traumaticin  of  the 
Pharmacopeia — i  vol.  guttapercha  dissolved  in  6  vols.  chloroform)  is 
diluted  before  use  with  25  vols.  of  chloroform  and  the  resulting  mixture 
poured  upon  a  slide.  The  latter  is  tilted,  and  after  evaporation  of  the 
chloroform,  heated  over  a  gas  flame.  The  paraffin  sections  are  mounted 
upon  the  slides  so  prepared  and  then  painted  with  a  solution  of  guncotton 
in  aceton  and  alcohol  (2  gm.  guncotton  dissolved  in  50  c.c.  of  aceton, 
5  c.c.  of  which  is  diluted  with  20  c.c.  of  absolute  alcohol).  After  painting 
with  this  solution,  the  sections  are  firmly  pressed  upon  the  slide  with 
tissue  paper,  and  after  drying  are  made  to  adhere  more  closely  by  slight 
warming.  Fixation  to  the  slide  with  water  is  equally  good.  The  sections 
can  now  be  treated  with  various  staining  solutions  without  becoming 
detached  from  the  slides.  The  paraffin  is  gotten  rid  of  by  immersing  in 
xylol,  after  which  the  specimens  are  placed  in  absolute  alcohol.  Fuchsin  S. 
can  be  used  as  a  stain  (20  gm.  fuchsin  S.  dissolved  in  100  c.c.  anilin 
water).  A  small  quantity  of  this  solution  is  placed  upon  the  section, 
and  the  slide  warmed  over  a  flame  until  its  lower  surface  becomes  quite 
perceptibly  warm  and  the  staining  solution  begins  to  evaporate.  The 
slide  is  then  allowed  to  cool,  washed  with  picric  acid  (concentrated 
alcoholic  solution  of  picric  acid  diluted  with  2  vols.  of  water),  after 
which  it  is  covered  with  a  fresh  quantity  of  picric  acid,  and  again,  but 
this  time  vigorously,  heated  (one-half  to  one  minute).  Occasionally 
the  same  results  can  be  obtained  by  covering  the  section  for  five  minutes 
with  a  cold  solution  of  picric  acid  of  the  above  strength.  This  last 
procedure  has  a  decided  influence  upon  the  granula,  and  gives  rise  to  a 
distinct  differentiation  between  them  and  the  remaining  portions  of  the 
cell,  the  latter  appearing  grayish -yellow,  while  the  granula  themselves 
appear  bright  red.  In  some  cases  where  the  granula  can  not  be  sharply 
differentiated  from  the  remaining  structures,  it  may  be  necessary  to 
repeat  the  staining  process.  Xylol -Canada  balsam  should  not  be  used 
for  mounting,  as  it  has  a  bleaching  effect  upon  the  osmic  acid  in  the 
specimen.  Mount  either  in  liquid  paraffin  (Altmann)  or  in  undiluted 
Canada  balsam,  which  is  easily  reduced  to  a  fluid  state,  whenever  needed, 
by  heating. 

There  is  another  method  used  by  Altmann  which  deserves  mention, 
but  practical  application  of  which  must  be  improved  upon  in  the  future ; 
this  consists  in  freezing  the  specimens  and  drying  them  for  a  few  days  in 
the  frozen  condition  in  a  vacuum  over  sulphuric  acid  at  a  temperature  of 
about  —30°  C. 

According  to  Fischer,  dilute  solutions  of  pepton  when  treated  with 
various  reagents  (especially  with  a  potassium  bichromate-osmium  mix- 
ture) form  precipitates  and  granules  which  are  remarkable  in  that  they 
react  to  stains  exactly  as  do  Altmann' s  granula.  It  is,  therefore,  doubt- 
ful whether  Altmann 's  granules  should  be  regarded  as  vital  structures. 

125.  Altmann  (92)  has  also  devised  a  simpler  negative  method  for 
demonstrating  the  granula.  Fresh  specimens  are  placed  for  twenty-four 
hours  in  a  solution  consisting  of  molybdate  of  ammonium  2.5  gm., 
chromic  acid  0.35  gm.,  and  water  100  c.c.  ;  then  treated  for  several 
days  with  absolute  alcohol,  sectioned  in  paraffin,  and  colored  with  a 
nuclear  stain  such  as  hematoxylin  or  gentian.  The  intergranular  network 
is  colored,  while  the  granula  remain  colorless.  The  amount  of  chromic 
acid  used  (0.25  to  i%)  varies  according  to  the  object  treated  ;  if  molyb- 
date of  ammonium  alone  be  used,  the  nuclei  will  appear  homogeneous, 


THE     TISSUES.  73 

while  if  an  excess  of  chromic  acid  be  employed,  the  nuclei  will  appear 
coarsely  reticulated.  This  method  leads  to  the  formation  of  granula  in 
the  cells  as  well  as  in  the  nucleus. 

126.  By  fixing  and  staining  cells  of  widely  different  vegetable  and 
animal  types  Blitschli  believes  he  has  demonstrated  the  existence  of  proto- 
plasmic structures  having  the  form  of  bubbles  and  termed  by  him  micro- 
scopic foam-structures.  Fixing  is  done  either  in  picric  acid  solution  or  in 
weakly  iodized  alcohol.  The  specimens  are  then  stained  with  iron-hema- 
toxylin — /.  <?.,  first  treated  with  acetate  of  iron,  rinsed  in  water,  and  trans- 
ferred to  a  0.5%  aqueous  solution  of  hematoxylin  (similar  to  the  method 
of  R.  Heidenhain  (vid.  T.  85).  Very  thin  sections  are  required  (^  to 
i  //).  Mounting  is  done,  when  the  lighting  is  good,  in  media  having 
low  refractive  indices,  which  emphasize  the  alveolar  or  foam -like  structure 
of  the  protoplasm.  Of  various  animal  objects,  Biitschli  especially  recom- 
mends young  ovarian  eggs  of  teleosts,  and  blood-cells  and  intestinal  epi- 
thelium of  the  frog,  etc.  It  is  still  a  matter  of  uncertainty  whether  or 
not  the  structures  are  actually  present  in  living  protoplasm. 


II.  THE  TISSUES. 

The  first  few  generations  of  cells  which  result  from  the  segmen- 
tation of  the  fertilized  ovum  have  no  pronounced  characteristics. 
They  are  embryonic  cells  of  rounded  form,  and  are  known  as  blas- 
tomeres.  As  they  increase  in  number  they  become  smaller  and  of 
polygonal  shape,  owing  to  the  pressure  to  which  they  are  subjected. 
From  the  mass  of  blastomeres,  known  as  the  nwrula  mass,  there 
are  formed,  under  various  processes  described  under  the  name  of 
gastndation,  two  layers  of  cells,  the  so-called  primary  germ  layers, 
of  which  the  outer  is  the  ectoderm,  the  inner  the  entoderm.  To  the 
primary  germ  layers  is  added  still  a  third  layer,  called  the  meso- 
dcnn ;  it  is  derived  from  both  the  ectoderm  and  entoderm,  but 
principally  from  the  latter.  From  these  three  layers  of  cells,  known 
as  the  primary  blastodermic  layers,  are  developed  all  the  tissues,  each 
layer  developing  into  certain  tissues  that  are  distinct  for  this  layer. 
In  their  further  development  and  differentiation  the  cells  of  the  blas- 
todermic layers  undergo  a  change  in  shape  and  structure  character- 
istic for  each  tissue,  and  there  is  developed  an  intercellular. substance 
varying  greatly  in  amount  and  character  in  the  several  tissues.  In 
the  tissues  developed  from  the  ectoderm  and  entoderm  the  cellular 
elements  give  character  to  the  tissue,  while  the  intercellular  sub- 
stance is  present  in  small  quantity ;  in  the  majority  of  the  tissues 
developed  from  the  mesoderm,  the  intercellular  substance  is  abun- 
dant, while  the  cellular  elements  form  a  less  conspicuous  portion. 

The  tissues  derived  from  the  ectoderm  are  : 

The  epidermis  of  the  skin,  with  the  epidermal  appendages  and 
glands  ;  the  epithelium  lining  the  mouth,  with  the  salivary  glands 
and  the  enamel  of  the  teeth  ;  the  epithelium  and  glands  of  the  nasal 
tract  and  the  cavities  opening  into  it ;  the  lens  of  the  eye  and  retina, 


74  .  THE     TISSUES. 

and  the  epithelium  of  the  membranous  labyrinth  of  the  ear  ;  and 
finally,  the  entire  nervous  system,  central  and  peripheral. 

From  the  entoderm : 

The  epithelium  lining  the  digestive  tract,  and  all  glands  in  con- 
nection with  it,  including  the  liver  and  pancreas  ;  the  epithelium  of 
the  respiratory  tract  and  its  glands  ;  the  epithelium  of  the  bladder 
and  urethra  (in  the  male,  only  the  prostatic  portion,  the  remainder 
being  of  ectodermal  origin). 

The  cells  of  the  mesoderm  are  early  differentiated  into  three 
groups  (Minot,  99)  : 

(a)  Mesothelium. — The  mesothelial  cells  retain  the  character  of 
epithelial  cells.      They  form  the  lining  of  the   pleural,    pericardial, 
and  peritoneal  cavities,  and  give  origin  to  the  epithelium  of  the  uro- 
genital  organs  (with  the  exception  of  the  bladder  and  urethra),  and 
striated  and  heart  muscle  tissue. 

(b)  Mesenchyme,  from  which  are  derived  all  the  fibrous  connective 
tissues,  cartilage,  and  bone,  involuntary  muscle  tissue,  the  spleen, 
lymph-glands,  and  bone-marrow  ;  and  cells  of  an  epithelioid  charac- 
ter, lining  the  blood   and  lymph-vessels  and  lymph-spaces,  known 
as  endothelial  cells. 

.     (c)  Mesameboid  cells,  comprising  all  red  and  white  blood-cells. 

It  would  be  extremely  difficult  to  attempt  a  classification  of  tis- 
sues according  to  their  histogenesis,  as  identical  tissue  elements  owe 
their  origin  to  different  germinal  layers.  The' classification  adopted 
by  us  is  based  rather  on  the  structure  of  the  tissues  in  their  adult 
stage. 

We  distinguish  : 

A.  Epithelial  tissues  with  their  derivatives. 

B.  Connective  tissues  ;  adipose  tissue  ;  supporting  tissues  (car- 
tilage, bone). 

C.  Muscular  tissue. 

D.  Nervous  tissue. 

E.  Blood  and  lymph. 


A.  EPITHELIAL  TISSUES. 

Epithelial  tissues  are  nonvascular,  and  composed  almost  wholly 
of  epithelial  cells,  united  into  continuous  membranes  by  a  substance 
known  as  intercellular  cement.  They  serve  to  protect  exposed 
surfaces,  and  perform  the  functions  of  absorption,  secretion,  and 
excretion. 

The  epithelia  are  developed  from  all  of  the  three  layers  of  the 
blastoderm. 

They  secrete  the  cement-substance  found  between  their  contigu- 
ous surfaces.  This  takes  the  form  of  thin  lamellae  between  the  cells, 
gluing  them  firmly  together.  In  certain  regions  the  epithelial  cells 
develop  short  lateral  processes  (prickles),  which  meet  like  structures 


EPITHELIAL    TISSUES.  75 

from  neighboring  cells,  thus  forming  intercellular  bridges.  Between 
these  bridges  are  intercellular  spaces  filled  with  lymph-plasma  for 
the  nourishment  of  the  cells.  Epithelia  do  not,  as  a  rule,  possess 
processes  of  any  length.  However,  it  would  appear  that  the  base- 
ment membranes,  situated  beneath  the  epithelia,  consist  chiefly  of 
processes  from  the  basal  portion  of  the  cells.  Some  authors  ascribe 
to  them  a  connective-tissue  origin,  a  theory  which  conflicts  with  the 
fact  that  such  membranes  are  present  in  the  embryo  before 
connective  tissue,  as  such,  has  been  developed  (membrana  prima, 
Hensen,  76). 

The  free  surfaces  of  epithelia  often  support  cuticnlar  structures 
which  are  to  be  regarded  as  the  products  of  the  cells.  The  cutic- 
ulae  of  neighboring  cells  fuse  to  form  a  cuticular  membrane  or  mar- 
ginal zone  which  can  be  detached  in  pieces  of  considerable  size 
(cuticula).  In  longitudinal  sections  the  cuticula  show,  in  many 
cases,  a  striation  which  would  seem  to  indicate  that  they  are  com- 
posed of  a  large  number  of  rod-like  processes  cemented  together  by 
a  substance  possessing  a  different  refractive  index.  The  cell-body  is 
also  striated  for  more  than  half  its  length,  corresponding  to  the  rods 
of  the  marginal  zone.  In  the  region  of  the  nucleus  at  the  basal  por- 
tion the  striation  disappears,  the  cell  here  consisting  of  granular  pro- 
toplasm of  a  more  indifferent  character. 

Since  one  surface  of  each  epithelial  layer  lies  free,  and  is  conse- 
quently exposed  to  other  conditions  than  the  inner  surface,  certain 
differences  are  noticed  between  the  two  ends  of  each  cell.  The 
cells  may  develop  cuticular  structures  as  above  stated.  In  other 
cases  motile  processes  (cilia)  are  developed  on  their  exposed  surface, 
which  move  in  a  definite  direction  in  the  medium  surrounding 
them,  and  by  means  of  this  motion  sweep  away  foreign  bodies.  It 
is  not  strange  that  the  free  surface  of  the  epithelia,  exposed  as  it  is 
to  stimulation  from  without,  should  develop  special  structures  for 
the  reception  of  sensations  (sense  cells). 

On  the  other  hand,  the  inner  or  basal  surfaces  of  the  cells  usually 
retain  a  more  indifferent  character,  and  serve  for  the  attachment  of 
the  cells  and  the  conveyance  of  their  nourishment.  For  this  reason 
the  nuclei  of  such  cells  are  usually  situated  near  the  basal  surface. 

From  the  above  it  is  seen  that  the  two  ends  of  the  epithelial  cell 
undergo  varying  processes  of  differentiation,  the  outer  being  adapted 
more  to  the  animal,  the  inner  more  to  the  vegetative  functions. 
This  differentiation  has  recently  been  known  as  the  polarity  of  the 
cell.  This  polarity  appears  to  be  retained  even  when  the  cell  loses 
its  epithelial  character  and  assumes  other  functions  (Rabl,  90). 

With  few  exceptions,  blood-  and  lymph-vessels  do  not  penetrate 
into  the  epithelia,  but  the  latter  are  richly  supplied  with  nerves. 
The  finer  morphology  of  the  epithelia  will  be  described  in  the  chap- 
ters on  the  different  organs  in  Part  II. 

Epithelia  are  classified  according  to  the  shape  and  relation  of 
the  epithelial  cells. 


76 


THE    TISSUES. 


We  give  the  following  classification  : 

1.  Simple  epithelia  (with  or  without  cilia). 

(a)  Squamous  epithelium. 

(b)  Cubic  epithelium. 

(c)  Columnar  epithelium. 

(d)  Pseudostratified  columnar  epithelium. 

2.  Stratified  epithelia  (with  or  without  cilia). 

(a)  Stratified  squamous  epithelium,  with  superficial 

flattened  cells  (without  cilia). 
($)   Transitional  epithelium. 
(c)   Stratified    columnar   epithelium,   with  superficial 

columnar  cells  (with  or  without  cilia). 

3.  Glandular  epithelium. 

4.  Neuro-epithelium. 


J.  SIMPLE  EPITHELIUM. 

In  simple  epithelia  the  cells  lie  in  a  single  continuous  layer. 
Simple  epithelia  are  very  widely  ^distributed.      They  line  almost 
the  entire  alimentary  tract,  the  smaller  respiratory  passages  and  air 


Fig.  36. — Isolated  cells  of  squamous  epithe- 
lium (surface  cells  of  the  stratified  squamous 
epithelium  lining  the  mouth)  :  a,  a,  Cells  present- 
ing under  surface  ;  b,  cell  with  two  nuclei. 


Fig-  37-  —  Surface  view  of 
squamous  epithelium  from  skin  of  a 
frog;  X  4°°-  Technic  No.  124. 


sacs,  the  majority  of  the  gland  ducts,  the  oviducts  and  uterus,  and  the 
central  canal  of  the  spinal  cord  and  ventricles  of  the  brain. 

(a)  Simple  Squamous  Epithelium. — In  simple  squamous  epi- 
thelium the  cells  are  flattened.  Their  contiguous  surfaces  appear 
regular,  forming,  when  seen  from  above,  a  mosaic.  The  nuclei  lie, 
as  a  rule,  in  the  middle  of  the  cell,  and  if  the  latter  be  very  much 
flattened,  the  position  of  the  nucleus  is  made  prominent  by  a  bulg- 
ing of  the  cell  at  this  point.  It  occurs  in  the  alveoli  of  the  lung. 

(fr)  Simple  Cubic  Epithelium. — Epithelial  cells  of  this  type 
differ  from  the  above  only  in  that  they  are  somewhat  higher.  They 
appear  as  short  polygonal  prisms.  Their  outlines  are,  as  a  rule,  not 
irregular,  but  form  straight  lines.  Cubic  epithelium  occurs  in  the 


EPITHELIAL    TISSUES. 


77 


smaller  and  smallest  bronchioles  of  the  lungs,  in  certain  portions  of 
the  uriniferous  tubules  and  their  collecting  ducts,  in  the  smaller 
ducts  of  salivary  and  mucous  glands,  liver,  pancreas,  etc. 

(c)  Simple  Columnar  Epithelium. — In  this  type  the  cells  take 
the  form  of  prisms  or  pyramids  of  varying  length.  Cuticular 
structures  are  especially  well  developed.  Columnar  epithelium 
occurs  in  the  entire  intestinal  tract  from  the  cardiac  end  of  the 
stomach  to  the  anus,  in  certain  portions  of  the  kidney,  etc. 


Goblet  cell. 


Cuticular  border. 


Fig.  38. — Simple  columnar  epithelium  from  the  small  intestine  of  man  :  a,  Isolated  cells  ; 
^,  surface  view  ;  c,  longitudinal  section. 

Simple  ciliated  columnar  epithelium  is  found  in  the  oviduct  and 
uterus,  central  canal  of  the  spinal  cord,  and  smaller  bronchi. 

(d)  Pseudostratified  Columnar  Epithelium. — This  type  is 
one  in  which  all  the  cells  rest  on  a  basement  membrane,  but  they 
are  so  placed  that  the  nuclei  come  to  lie  in  different  planes.  Thus, 
in  a  longitudinal  section  the  nuclei  are  seen  to  be  placed  in  several 
rows. 

The  development  of  this  type  from  the 
simpler  forms  occurs  when  the  cells  are  too 
crowded  to  retain  their  normal  breadth.  As 
a  result,  they  become  pyramidal,  alternate 
cells  resting  their  bases  or  apices  on  the  base- 
ment membrane.  As  the  nucleus  is  usually 
situated  at  the  broader  portion  of  the  cell, 
the  result  is  that  there  are  two  rows  of  nu- 
clei simulating  a  stratified  epithelium.  Occa- 
sionally there  are  spindle-shaped  cells  wedged  in  between  the  pyra- 
midal cells,  and  as  the  broad  portion  of  these  cells  is  midway 
between  the  basement  membrane  and  external  surface,  a  third  row 
of  nuclei  is  seen  midway  between  the  other  two.  Such  epithelia 
usually  possess  cilia  (portions  of  the  respiratory  passages). 


Fig-  39.— Diagram 
of  pseudostratified  col- 
umnar epithelium. 


2.  STRATIFIED  EPITHELIUM. 

Should  the  increase  of  the  cells  forming  the  last  type  of  simple 
epithelium  proceed  to  such  an  extent  that  all  the  cells  no  longer 
rest  on  the  basement  membrane,  an  epithelium  is  formed  having  dis- 


THE     TISSUES. 


Fig.  40. — Schematic 
diagram  of  stratified  pave- 
ment epithelium. 


tinct  layers  of  cells — a  stratified  epithelium.  It  is  clear  that  all  the 
cells  of  a  stratified  epithelium  can  not  be  equally  well  nourished  by 
the  blood-supply  from  the  vessels  in  the 
highly  vascular  connective  tissue  beneath. 
The  middle  and  outer  layers  of  cells  accord- 
ingly suffer.  The  deeper  layers  are  much 
better  nourished,  and  as  a  consequence  their 
cells  increase  much  more  rapidly  than  those 
above  ;  they  push  outward,  replacing  the 
superficial  cells  as  fast  as  they  die  or  are 
thrown  off.  The  proliferation  of  cells  in  a 
stratified  epithelium  occurs,  therefore,  chiefly 
in  its  basal  layers. 

(a)  Stratified  Squamous  Epithelium. — Stratified  squamous 
epithelium  with  superficial  flattened  cells  forms  the  epidermis  with 
its  continuations  into  the  body,  as,  for  instance,  the  walls  of  the  oral 
cavity  and  the  esophagus,  the  epithelium  of  the  conjunctiva,  the 
vagina,  the  external  auditory  canal,  and  the  external  sheath  of  the 
hair  follicles. 

The   cells  of  the  basal  layer  are  here  mostly  cubic-cylindric. 
Then  follow,  according  to  the  situation   of  the  epithelium,  one   or 
more  layers  of  polyhedral  cells,  which  become  gradually  flattened 
toward    the  surface,   the    outer-     ^^  ^^^ 
most   layers    consisting   of   thin     £* 
plate-like  cells. 

In  stratified  squamous  epi- 
thelia,  where  the  oute.r  cells  be-  »£^ 
come  horny  (as  in  the  skin),  the 
stratification  is  still  more  special- 
ized. Here  layers  are  inserted 
in  which  the  horny  or  chitinous 
substance  is  gradually  formed, 
although  the  cells  do  not  be- 
come chitinous  until  the  super- 
ficial layers  are  reached. 

Especially  characteristic  of 
stratified  squamous  epithelium  is 
the  arrangement  of  the  connec- 
tive tissue  on  which  this  epithe- 
lium rests.  There  are  cone-like 
projections,  known  as  papillce, 
arising  from  the  connective  tissue 
beneath  the  epithelium,  project- 
ing into  the  latter  in  such  a  way  that  on  cross-section  the  junction 
of  the  two  tissues  appears  as  a  wave-like  line.  These  papillae  not 
only  serve  to  fasten  the  epithelium  more  firmly  to  the  connective  tissue 
below,  but  influence  very  favorably  the  nourishment  of  the  former  by 
allowing  a  greater  number  of  its  basal  cells  to  approximate  the  under- 


Fig.  41. — Cross  -  section  of  stratified 
squamous  epithelium  from  the  esophagus 
of  man. 


EPITHELIAL    TISSUES. 


79 


lying  blood-capillaries.  The  pyramidal  extensions  of  the  epithelium 
between  the  papillae  are  designated  interpapillary  epithelial  processes. 
In  regions  where  the  stratified  squamous  epithelium  consists  of 
many  layers,  the  prickle  cells,  intercellular  bridges,  and  the  inter- 
cellular spaces  are  especially  well  developed.  These  spaces  facili- 
tate the  passage  of  the  lymph-plasma  to  the  more  superficial  layers 
of  cells. 

(&)  Transitional  Epithelium. — Transitional  epithelium  is  a 
stratified  epithelium  occurring  in  the  pelvis  of  the  kidney,  the  ure- 
ters, bladder,  and  the  posterior  portion  of  the  male  urethra.  It  is 
composed  of  four  to  six  layers  of  cells  and  rests  on  a  connective 
tissue  free  from  papillae.  In  sections  the  cells  of  the  deeper  layers 
appear  to  be  of  irregularly  columnar,  cubic  or  triangular  shape.  The 


Fig.  42. — -Isolated  transitional  epithe- 
lial cells  from  the  bladder  of  man  :  a,  o, 
c,  d,  Large  surface  cells,  t-and  d  presenting 
the  pitted  undersurface  ;  e,  variously  shaped 
cells  from  the  deeper  layers. 


Fig.  43. — Cross-section  of  transitional 
epithelium  from  the  bladder  of  a  young 
child. 


cells  forming  the  superficial  layer  are  large,  somewhat  flattened  cells, 
with  convex  free  surfaces,  often  possessing  two,  sometimes  three, 
nuclei.  They  cover  a  number  of  the  cells  of  the  layer  just  beneath 
them,  their  under  surfaces  being  pitted  to  receive  the  upper  ends  of 
the  deeper  cells.  In  teased  preparations  the  cells  of  the  deeper 
layers  appear  very  irregular,  often  showing  ridges  or  variously 
shaped  processes.  (See  Fig.  42.) 

(c)  Stratified  Columnar  Epithelium. — In  this  type  the  super- 
ficial layer  consists  of  columnar  cells,  the  basal  ends  of  which  are 
usually  somewhat  pointed,  or  may  branch.  The  deeper  cells,  which 
may  be  arranged  in  one  or  more  layers,  are  of  irregular,  triangular, 
polyhedral,  or  spindle  shape.  It  is  found  in  the  larger  gland  ducts, 
olfactory  mucous  membrane,  palpebral  conjunctiva,  portions  of  the 


8o 


THE    TISSUES. 


male  urethra  and  the  vas  deferens,  and  in  certain  regions  of  the 
larynx. 

The  ciliated  variety  of  this  epithelium  differs  from  the  foregoing 
in  that  the  superficial  columnar  cells  are  provided  with  cilia.  Strati- 
fied ciliated  columnar  epithelium  is  found  in  the  respiratory  portion 


Fig.  44.  —  Schematic  dia- 
gram of  stratified  columnar  epi- 
thelium. 


Fig.  45. — Ciliated  cells  from  the  bronchus  of  the 
dog,  the  left  cell  with  two  nuclei ;  X  DO°-  Technic 
No.  126. 


of  the  nose,  larynx,  trachea,  and  larger  bronchi,  in  the  Eustachian 
tube,  epididymis,  and  a  portion  of  the  vas  deferens. 

All  epithelial  cells  are  probably  joined  together  by  short  pro- 
cesses forming  intercellular  bridges,  the  lymph  supplying  them  with 
nourishment  circulating  in  the  intercellular  spaces  thus  formed. 
Toward  the  surface,  these  intercellular  spaces  are  roofed  over,  thus 
preventing  the  escape  of  the  fluid.  When  seen  from  the  surface, 
epithelia  treated  by  certain  methods  (iron-hematoxylin)  show  the 
cells  joined  together  by  very  minute,  clearly  defined  and  continuous 

Goblet  cell. 


-Cilia. 


Fig.  46. — Cross-section  of  stratified  ciliated  columnar  epithelium  from  the 
trachea  of  a  rabbit. 


cement-lines.  Bonnet  has  called  them  terminal  ledges,  or  bars 
(Schlussleisten).  The  function  of  this  structure  would  seem  to 
consist  in  its  power  to  prevent  the  escape  of  lymph  from  the  sur- 
face, and  the  penetration  of  micro-organisms  (M.  Heidenhain,  92  ; 
Bonnet,  95). 


EPITHELIAL    TISSUES. 


81 


3.  GLANDULAR  EPITHELIUM. 

(a)  The  Gland-cell. — Certain  cells  lying  scattered  among  other 
epithelial  cells  produce  substances  that  are  extruded  and  utilized  in 
the  body  economy.  The  protoplasm  of  such  a  cell  elaborates  in 
its  interior  a  substance  that  takes  the  form  of  vacuoles  or  granules, 
which  gradually  distend  the  cell ;  the  substance  thus  produced  is 
finally  given  off  as  the  secretion.  All  these  phases  of  the  activity 
of  a  gland-cell  are  included  under  the  term  secretion. 

Isolated  glandular  cells  are  frequently  met  with  in  epithelia,  and 
are  known  in  general  as  unicellular  glands.  They  occur  especially 
in  the  intestinal  and  respiratory  epithelium,  where,  owing  to  their 
shape,  they  are  termed  goblet  cells.  All  the  intestinal  epithelial  cells 
and  many  of  the  cells  of  respiratory  epithelium,  have  the  power  of 
changing  into  goblet  cells.  These  are  distinguished  from  the  neigh- 
boring cells  by  the  fact  that  their  free  ends  are  clearer  and  more 


Cilia. 


Mucin.    - 


Nucleus 


Basal  process.  -- 


Fig.  47. — Goblet  cells  from  the  bronchus  of  a  dog.  The  middle  cell  still  possesses 
its  cilia  ;  that  to  the  right  has  already  emptied  its  mucous  contents  (collapsed  goblet  cell) ; 
X  600.  Technic  No.  128. 

vesicular,  while  their  basal  portions,  containing  the  nuclei,  are  narrow 
and  pointed.  The  clear  substance  elaborated  by  the  protoplasm  of 
the  cell,  but  not  yet  extruded,  is  mucin.  On  closer  examination  it 
is  seen  that  this  substance  fills  the  interspaces  of  a  very  fine  proto- 
plasmic network  continuous  with  the  protoplasm  surrounding  the 
nucleus. 

Thus  we  have,  during  the  phases  of  secretion,  two  distinct  sub- 
stances in  the  cell-body  :  the  one  the  original  protoplasm  of  the  cell 
— protoplasm  (Kupffer)  ;  the  other  its  product,  in  this  case  mucin — 
paraplasm  (Kupffer).  When  the  secretion  is  extruded  the  goblet 
cell  collapses  and  then  appears  as  a  thin  cord  between  the  neighbor- 
ing cells.  There  is  as  yet  some  question  as  to  whether  a  collapsed 
goblet  cell  dies  after  the  expulsion  of  its  contents,  or  whether  it 
may  again  become  stored  with  mucin.  Should  it  be  destroyed,  its 
place  is  soon  occupied  by  the  closing  in  of  contiguous  cells. 
6 


82 


THE    TISSUES. 


Multicellular  glands  originate  by  the  metamorphosis  of  a  num- 
ber of  adjacent  cells  into  glandular  cells.  This  is  usually  accom- 
panied by  a  more  or  less  marked  dipping  down  of  the  epithelial 
layer  into  the  underlying  connective  tissue.  The  simplest  form  of 
such  an  invagination  is  a  cylindrical  tube  lined  entirely  by  glandular 
cells.  A  further  differentiation  may  take  place  in  that  all  the  in- 
vaginated  cells  do  not  assume  a  secretory  function,  those  at  the 
upper  portion  of  the  tube  forming  the  lining  membrane  of  an  excre- 
tory duct.  The  originally  uniform  tube  is  thus  differentiated  into 
an  excretory  and  a  secretory  portion. 

Multicellular  glands  may  lie  entirely  within  the  epithelium,  and  are 
then  known  as  intra-epithelial  glands,  in  contrast  to  the  extra-epithe- 
lial or  ordinary  type,  the  greater  part  of  which  lies  imbedded  in  the  under- 


£| Lumen  of  gland. 


=U>  Gland-cells. 


—  T.  propria. 
Muse,  mucosae. 


Fig.  48. — Simple  tubular  glands.     Lieberkiihn's  glands  from  the  large  intestine  of  man. 
Sublimate  fixation ;  X  9°- 

lying  connective  tissue.  Glands  of  the  former  type  have  been  studied  in 
amphibian  larvae,  and,  according  to  Sigmund  Mayer,  occur  also  in  the 
epididymis,  conjunctiva,  etc.,  of  mammals. 

(b)  General  Consideration  of  the  Structure  and  Classifica- 
tion of  Glands. — Variations  in  glandular  types  affect  principally 
the  secretory  portions  of  glands,  while  the  excretory  ducts  are  more 
or  less  uniform.  Glands  are  classified,  according  to  their  shape, 
into  tubular  and  saccular  glands  ;  each  of  these  types  is  further 
divided  into  simple  and  compound  tubular,  and  simple  and  com- 
pound saccular  (racemose)  glands. 

Tubular  Glands. — The  simplest  form  is  a  tubule  of  uniform 
diameter,  as  in  the  simple  tubular  glands  of  the  cardiac  region  of 


EPITHELIAL    TISSUES. 


the  stomach  and  in  the  crypts  of  Lieberkiihn  in  the  intestine. 
Without  losing  the  shape  of  a  tubule,  the  glands  of  this  type  may 
be  more  or  less  coiled  (pyloric  glands,  sweat  glands,  and  the  ceru- 


Excretory 
duct. 


Fig.  49. — Excretory  ducts 
and  lumina  of  the  secretory 
portion  of  a  compound  tubular 
gland.  Lingual  gland  of  the 
rabbit.  Chrome-silver  prepara- 
tion;  x  215- 


Fig.  50. — Lumina  of  the  secreting 
portion  of  a  reticulated  tubular  gland  ; 
from  the  human  liver.  Chrome-silver 
preparation  ;  X  1 2O- 


minous  glands  of  the  external  ear).  Again,  the  secretory  portions 
of  the  glands  may  divide,  forming  branched  tubular  glands  (pyloric 
glands,  uterine  glands). 

A  compound  tubular  gland  is  one  in  which  two  or  more  secre- 
tory  tubules   empty  into   each  branch  of  a  system    of  excretory 


Lumen 
and 
duct. 


Alveus. 


Alveus.         Alveolus.    Alveolus. 


Alveus. 


Tubule. 


Fig.  51. — Schematic  diagram  of  glandular  classification:  a,  Simple  tubular;  by 
branched  tubular  ;  c,  simple  alveolar ;  </,  compound  alveolar  (without  alveoli)  ;  e  and 
ft  alveolar  (with  alveoli). 

ducts,  as  the  result  of  repeated  division  of  the  primary  duct  (kid- 
ney). The  secretory  tubules  may  anastomose  with  each  other, 
forming  a  reticulated  tubular  gland  (liver). 


84  THE     TISSUES. 

In  alveolar  or  saccular  glands  the  secretory  portion  usually 
takes  the  form  of  a  winding  tube,  the  caliber  of  which  is  somewhat 
enlarged  at  its  extremity  (alveus). 

Glands  of  this  class  are  divided  into  simple  and  compound 
types,  as  in  the  case  of  the  tubular  glands.  To  the  former  belong 
Ebner's  glands  of  the  tongue  and  Brunner's  glands  of  the  duode- 
num ;  to  the  latter,  the  salivary  and  the  larger  mucous  glands. 

Certain  glands  have  the  shape  of  a  flask,  the  neck  representing 
the  excretory  duct  of  the  gland  (integumentary  glands  of  salaman- 
dra).  To  these  the  term  saccular  is  often  restricted.  Still  more 
complicated  forms  of  alveolar  or  saccular  glands  are  produced  by 
the  bulging  here  and  there  of  the  walls  of  the  tube  or  alveus. 
The  protrusions  thus  formed  are  known  as  alveoli. 

According  to  the  above  description,  multicellular  glands  may 
be  classified  as  follows  : 

Glands. 
Tubular.  Alveolar  or  saccular. 

Simple.  Compound      (here         Simple    (with    or         Compound      (with 

belong  also  the  reticu-     without  alveoli).  or  without  alveoli), 

lated  glands). 

The  secretory  and  excretory  epithelia  rest  upon  a  thin  membrane 
(membrana  propria),  which  has,  according  to  some  authors,  a  con- 
nective-tissue origin,  while,  according  to  others,  it  is  the  product  of 
the  glandular  cells  themselves.  In  some  cases  it  appears  structure- 
less, in  others  a  cellular  structure  can  be  distinguished  ;  in  the  latter 
case  the  cells  are  flattened,  with  very  much  flattened  nuclei,  and 
show  irregular  outlines. 

Macroscopically,  compound  glands  present  a  more  or  less  lobular 
structure,  the  separate  lobules  being  held  together  by  connective 
tissue.  In  the  immediate  neighborhood  of  the  gland  and  its  larger 
lobes,  the  connective  tissue  is  thickened  to  form  the  so-called  tunica 
albuginea  or  capsule.  In  this  fibrous-tissue  sheath  are  found  numer- 
ous blood-vessels  which  penetrate  between  the  lobes  and  lobules  of 
the  gland  and  form  a  dense  capillary  network  about  the  tubules  and 
alveoli  immediately  beneath  the  membrana  propria.  Nerve-fibers 
are  also  plentiful. 

(c)  Remarks  on  the  Process  of  Secretion. — The  gland-cell 
varies  in  its  microscopic  appearance  according  to  its  functional  con- 
dition. In  its  phases  of  activity  it  shows  vacuoles  filled  with  secre- 
tion (as  in  the  liver-cell),  or  a  granulation  (pancreas),  or  even  a  dis- 
tinct striation  of  its  protoplasm  (kidney). 

The  secretory  process  varies.  In  one  case  the  cell  remains 
intact  throughout  the  process  (salivary  glands) ;  in  another  a  por- 
tion of  its  own  substance  is  used  up  in  the  production  of  the  secre- 
tion, only  the  basal  portion  containing  the  nucleus  being  preserved. 
When  this  occurs,  the  upper  part  of  the  cell  is  reconstructed  from 
the  remaining  basal  portion,  and  the  cell  is  ready  to  renew  the 


EPITHELIAL   TISSUES.  85 

process  (mammary  glands).  In  a  third  type  the  whole  cell  is 
destroyed,  and  is  replaced  by  an  entirely  new  cell  (sebaceous 
glands). 

4.  NEURO-EPITHELIUM. 

In  certain  of  the  organs  of  special  sense  (inner  ear  and  taste-buds) 
the  epithelial  cells  about  which  the  nerves  terminate  undergo  a  high 
degree  of  specialization.  This  differentiation  is  more  apparent  in  the 
outer  portions  of  these  cells,  resulting  in  the  formation  of  one  or  sev- 
eral stiff,  hair-like  processes,  which  appear  especially  receptive  to 
stimuli.  Such  cells  are  known  as  neuro-epithelial  cells.  In  the 
epithelia  in  which  they  occur  they  are  surrounded  by  supporting 
or  sitstentacular  cells. 


5.  MESOTHELIUM  AND  ENDOTHELIUM. 

The  pleural,  pericardial,  and  peritoneal  cavities  are  lined  by 
a  single  layer  of  flattened  epithelioid  cells  which  develop  from  the 
mesothelium  lining  the  primitive  body  cav- 
ity (celom).  For  this  reason,  as  has  been 
suggested  by  Minot  (90),  the  term  mesothe- 
lium may  with  propriety  be  applied  to  this 
layer  in  its  developed  condition.  A  meso- 
thelial  cell  is  a  very  much  flattened  cell, 
resembling  those  of  squamous  epithelium, 
with  faintly  granular  protoplasm,  possessing 
a  flattened,  oval,  or  nearly  round  nucleus. 
These  cells  are  of  polyhedral  shape,  and 
are  united  into  a  single  layer  by  a  small 
amount  of  intercellular  cement  substance. 
The  borders  of  these  cells  may  be  quite 

regular    or    slightly    wavy    (Fig.    52)  ;    more       Silver    nitrate     preparation, 

often  they  are  serrated  (Figs.  53,  54).    The      stained  in  hematoxylin. 

quantity  of  intercellular  cement   substance 

is  so  small  in  amount,  and  the  cell  boundary  so  indistinct,  that 

it  is  necessary  to  resort  to  special  staining  methods  to  bring  out 

clearly  their  outline  (silver   nitrate  or  intra  vitam  methylene-blue 

method). 

The  cavities  lined  by  mesothelium  communicate  directly  with 
lymph-vessels  or  -spaces  beneath  the  lining  membrane  by  means  of 
small  openings  known  as  stomata.  The  stomata  are  surrounded  by 
a  layer  of  cubical  cells  with  granular  protoplasm,  spoken  of  as  ger- 
minal cells.  They  are  numerous  in  the  diaphragm,  and  may  be 
readily  demonstrated  in  the  frog  in  the  membrane  separating  the 
abdominal  lymph-space  from  the  peritoneal  cavity  (in  the  region 
of  the  kidneys).  Small  accumulations  of  the  intercellular  cement 
substance,  found  at  the  place  of  union  of  several  mesothelial  cells, 
are  described  as  pseudostomata  or  stigmata. 


86 


THE     TISSUES. 


Endothelial  cells  are  differentiated  mesenchymal  cells.    They  line 
the  blood-  and  lymph-vessels  and  lymph-spaces  (arachnoidal  and 


Nu- 
cleus. 


Fig.  53- — Mesothelium  from  mesentery  of       Fig.  54. — Mesothelium  from  peritoneum  of 
rabbit.  frog  ;   X  4°°-     Technic  No.  123. 


ig-  55. — Mesothelium  covering  posterior  abdominal  wall  of  frog.     Stained  with  silver 
nitrate  and  hematoxylin. 


c; 
V 


Fig.  56. — Endothelial  cells  from  small  artery  of  the  mesentery  of  a  rabbit.     Stained  with 
silver  nitrate  and  hematoxylin. 


synovial   spaces,  anterior  chamber  of  the  eye,   bursae,  and  tendon 
sheaths).     Endothelial  cells  are  in  structure  like  those  of  the  meso- 


EPITHELIAL    TISSUES.  8/ 

thelium.  In  blood-  and  lymph-vessels  they  are  of  irregular,  oblong 
shape,  with  serrated  borders.  The  boundaries  of  these  cells  are 
clearly  brought  out  by  silver  nitrate. 

TECHNIC. 

127.  Epithelium  may  be  examined  in  a  fresh  condition.     The  sim- 
plest method  consists  in  placing  some  saliva  under  a  cover-glass   and 
examining  it  with  a  moderate  power.      In  it  will  be  found  a  number  of 
isolated  squamous  epithelial  cells,  suspended  in  the  saliva  singly  and  in 
groups.     The  cells  that  are  cornified  still  show  the  nucleus  and  a  small 
granular  area  of  protoplasm. 

128.  In  order  to  examine  isolated  epithelial  cells  of  organs,  it 
is  necessary  to  treat  the  epithelial  shreds  or  whole  epithelial  layers  with 
the  so-called  isolating  or  maceration  fluids.      These  are:      (i)   Iodized 
serum;    (2)   very  dilute  osmic  acid   (0.1%   to  0.5%);   (3)  very  weak 
chromic  acid  solution  (about  1:5000  of  water)  ;  (4)  0.5%  or  1%  solution 
of  ammonium  or  potassium  bichromate  ;  and,  above  all,  the  one-third 
alcohol  recommended  by  Ranvier   (28  vols.   absolute  alcohol,  72  vols. 
distilled  water).     The  mixture  recommended  by  Soulier  (91),  consist- 
ing of  sulphocyanid  of  potassium  or  ammonium,   and  the  mixture  of 
Ripart  and  Petit  (vid.  T.  13)  serve  the  same  purpose.     All  these  solu- 
tions are  used  by  allowing  a  quantity  of  the  isolation  fluid  to  act  upon 
a  small  fresh  piece  of  epithelium  for  from  twelve  to  twenty -four  hours, 
according  to  the   temperature  of  the  medium  and   quality  of  the  tis- 
sue.     As  soon  as  the  isolation  fluid  has  done  its  work,  it  is  easy  to  com- 
plete the  isolation  of  the  cells  by  shaking  the  specimen  or  teasing  it  with 
needles.       Separation  of    the  elements  may  be  accomplished  either  in 
the  isolation  solution  itself  or  in  a  so-called  indifferent  fluid  (vid.  T.  13), 
or  in  gum -glycerin  (vid.  T.  98).     The  macerated  preparation  may  be 
stained  in  a  hematoxylin  or  carmin  solution  before  teasing  and  mounting 
in  gum-glycerin. 

129.  The  movement  of  the  cilia  can  be  observed  in  mammalian  tissues 
by  scraping  the  epithelium  from  the  trachea  with  a  scalpel  and  examining  it 
in  an  indifferent  fluid.     As  the  ciliated  epithelium  of  mammals  is  very 
delicate  and  sensitive,  specimens  with  a  longer  duration  of  ciliary  move- 
ment are  more  desirable.     They  can  be  obtained  by  using  the  mucous 
membrane  from  the  palate  of  a  frog  (examine  in  normal  salt  solution,  vid. 
T.  13).      Particularly  large  epithelial  cells,  as  well  as  very  long  cilia,  are 
found  on  the  gill -plates  of  mussels  or  oysters. 

130.  In  order  to  study  the  relations  of  mesothelial  and  endothe- 
lial  cells,  the  silver  method  is  the  most  satisfactory.     The  outlines  of  the 
mesothelial  cells  may  be  clearly  brought  out  by  placing  pieces  of  the  peri- 
cardium, central  tendon  of  the  diaphragm,  or  the  mesentery  in  a  o.  75  c/c  to 
i  %  solution  of  silver  nitrate.     Before  placing  in  this  solution,  they  should 
be  rinsed  in  distilled  water  in  order  to  remove  any  adherent  foreign  bodies, 
such  as  blood-corpuscles,  etc.     In  this  solution  they  remain  until  opaque, 
which  occurs  in  from  ten  to  fifteen  minutes.     They  are  then  again  rinsed 
with  distilled  water,   in  which  they  are  exposed  to  sunlight  until   they 
begin  to  assume  a  brownish -red  color.      Once  again  they  are  washed  with 
distilled  water,   and  either  placed  in  glycerin,   in  which  they  may  be 
mounted,  or  dehydrated  and  mounted  in  Canada  balsam,  according  to  the 


88  THE     TISSUES. 

usual  methods.  The  margins  of  the  cells  subjected  to  this  treatment  will 
appear  black. 

Endothelial  cells  may  be  demonstrated  after  the  following  method  : 
A  small  mammal  (rat,  Guinea-pig,  rabbit,  or  cat)  is  narcotized.  Before 
the  heart's  action  is  completely  arrested,  the  thorax  is  opened  and  the 
heart  incised.  As  soon  as  the  blood  stops  flowing,  a  cannula  is  inserted 
and  tied  in  the  thoracic  aorta  a  short  distance  above  the  diaphragm,  and 
50  to  80  c.c.  of  a  \°]0  aqueous  solution  of  silver  nitrate  injected  through 
the  cannula.  About  fifteen  minutes  after  the  injection  of  the  silver  nitrate 
solution,  there  is  injected  through  the  same  cannula  100  to  150  c.c.  of  a 
4%  solution  of  formalin  (formalin  10  parts,  distilled  water  90  parts). 
The  abdominal  cavity  is  then  opened,  loops  of  the  intestine  with  the 
attached  mesentery  removed  and  placed  in  a  4%  solution  of  formalin,  in 
which  the  tissue  is  exposed  to  the  sunlight.  As  soon  as  the  reduction  of 
the  silver  nitrate  has  taken  place,  which  is  easily  recognized  by  the  reddish- 
brown  color  assumed  by  the  tissues,  the  mesentery  is  divided  into  small 
pieces,  dehydrated  first  in  95%,  then  in  absolute  alcohol,  cleared  in  oil 
of  bergamot,  and  mounted  in  balsam.  As  a  rule,  the  mesothelial  cells 
covering  the  two  surfaces  of  the  mesentery,  and  the  endothelial  cells 
lining  the  arteries,  veins,  and  capillaries  are  clearly  outlined  by  the 
reduced  silver  nitrate. 

If  desired,  the  tissue  may  be  further  stained  in  hematoxylin  (we  have 
used  Bohmer's  hematoxylin  solution)  or  in  a  carmin  solution  after  dehy- 
dration in  95%  alcohol,  after  which  they  are  dehydrated,  cleared,  and 
mounted  in  balsam.  In  preparations  made  after  this  method  the  endo- 
thelial cells  are  outlined  by  fine  lines  of  dark  brown  or  black  color. 

Silver  nitrate  may  also  be  dissolved  in  a  2  %  to  3  %  solution  of  nitric 
acid,  in  osmic  acid,  and  various  other  fluids.  Stratified  epithelia  can 
also  be  impregnated  with  silver  nitrate,  but  only  after  prolonged  immer- 
sion. They  are  exposed  to  sunlight  after  sectioning  on  the  freezing 
microtome,  or  after  hardening  and  imbedding,  followed  by  sectioning. 
After  the  reduction  of  the  silver  the  sections  are  dehydrated  and  mounted 
in  balsam. 

131.  Kolossow  has  devised  the  following  excellent  method  for  demon- 
strating intercellular  bridges  :     Fine  membranes,  or  even  minute  frag- 
ments of  previously  fixed  tissues,  are  placed  for  about  a  quarter  of  an  hour 
in  a  0.5%  to  i%  osmic  acid  (or  in  a  mixture  composed  of  50  c.c.  abso- 
lute alcohol,  50  c.c.  distilled  water,  2  c.c.  concentrated  nitric  acid,  and 
i  to  2  gm.  osmic  acid)  and  then  into  a  io%  aqueous  solution  of  tannin 
for  five  minutes,  or  into  a  developer  consisting  of  the  following :  water, 
450  c.c.  ;   85%   alcohol,  100  c.c.  ;  glycerin,  50  c.c.  ;  purified  tannin, 
30  gm.,  and  pyrogallic  acid,  30  gm.      In  the  latter  case  they  are  subse- 
quently rinsed  in  a  weak  solution  of  osmic  acid,  washed  with  distilled 
water,  and  then  carried  over  into  alcohol. 

132.  There  are,  of  course,  special  methods  of  fixing  and  subsequently 
examining  epithelial  structures ;    these,  and  the  methods  of  examining 
gland  tissue,  will  be  discussed  in  the  chapters  devoted  to  the  various 
organs. 


THE    CONNECTIVE    TISSUES.  89 


B.  THE  CONNECTIVE  TISSUES. 

In  the  connective  tissues,  the  intercellular  substance  gives  char- 
acter to  the  tissue,  the  cellular  elements  forming  a  less  conspicuous 
portion.  All  the  members  of  this  group  are  developed  from  the  mes- 
enchyme,  an  embryonic  tissue  differentiated  early  in  embryonic  life 
from  the  mesoderm,  and  consisting  of  variously  branched  cells, 
possessing  a  small  amount  of  protoplasm  and  relatively  large  nuclei. 
The  branches  of  neighboring  cells  are  united  by  threads  of  proto- 
plasm ;  between  the  cells  is  found  a  homogeneous  ground-substance 
or  matrix. 

In  their  fully  developed  condition  some  of  the  members  of  the 
connective-tissue  group  are  only  slightly  altered  from  embryonic  con- 
nective tissue.  This  is  the  case  in  mucous  connective  tissue,  which 


—  Cell  process. 


Nucleus. 


Fig-  57. — Mesenchymatous  tissue  from  the  subcutis  of  a  duck  embryo  ;  X  650. 
Technic  No.  17. 

resembles  closely  mesenchymal  tissue.  In  other  members  there 
are  developed  in  the  ground-substance,  in  less  or  greater  number, 
fibers,  known  as  connective -tissue  fibers,  thus  forming  reticular  con- 
nective tissue  and  the  looser  and  denser  forms  of  fibrous  connective 
tissue.  A  more  marked  condensation  of  the  intercellular  substance 
is  observed  in  cartilage  ;  and  in  bone  and  dentin  a  still  greater  de- 
gree of  density  is  obtained  by  the  deposition  of  calcareous  salts  in 
the  intercellular  matrix. 

The  role  played  by  the  connective  tissues  in  the  economy  of  the 
body  is  largely  passive,  depending  on  their  physical  properties. 
Bone  and  cartilage  serve  as  supporting  tissues  ;  the  looser  fibrous  tis- 
sues for  binding  and  holding  the  organs  and  parts  of  organs  firmly 
in  place.  The  denser  fibrous  connective  tissues  come  into  play 


90  THE    TISSUES. 

where  strength  and  pliability  are  desired,  as  in  ligaments,  or  else  are 
used  in  the  transmission  of  muscular  force,  as  in  tendons. 

Another  important  characteristic  of  connective  tissue  is  that  its 
various  members  are  capable  of  undergoing  transformation  into 
wholly  different  types  ;  bone,  for  instance,  being  developed  from 
fibrous  connective  tissue  and  from  cartilage.  Certain  structures  are 
represented  by  different  members  of  the  connective-tissue  group  in 
the  different  classes  of  vertebrates.  In  certain  fishes  the  skeleton  is 
cartilaginous,  and  in  certain  birds  the  leg  tendons  are  formed  of 
osseous  tissue,  etc. 

In  the  different  types  of  connective  tissue  the  cellular  elements 
are  morphologically  very  similar,  and  do  not  differ  materially  from 
the  mesenchymal  cells  from  which  they  are  developed. 

The  connective  tissues  receive  their  nutrition  from  the  lymph. 
In  the  denser  connective  tissues  this  permeates  the  tissues  through 
clefts  or  spaces  in  the  ground-substance,  in  which  the  connective- 
tissue  cells  are  found  and  which  are  united  by  means  of  fine  canals 
into  a  canalicular  system.  In  the  looser  fibrous  tissues  and  in 
mucous  connective  tissue  the  system  of  lymph-channels  is  not 
present ;  here  the  lymph  seems  to  pass  through  the  ground-sub- 
stance. 

Certain  connective-tissue  cells  have  the  function  of  producing  fat. 
In  various  parts  of  the  body,  masses  of  fat  tissue  are  formed  as  a 
protection  to  various  organs  and  as  a  reserve  material  upon  which 
the  body  can  call  when  necessary.  This  type  can  hardly  _be  con- 
sidered a  separate  class  of  connective  tissues,  as  it  can  be  demon- 
strated that  it  is  merely  modified  connective  tissue,  and  can  occur 
wherever  the  latter  is  found. 

Finally,  certain  elements  of  the  middle  germinal  layer  are  capa- 
ble of  producing  colored  substances  known  as  pigments.  To  this 
class  belong  the  pigment  cells  and  the  red  blood-corpuscles. 

From  the  above  account  it  will  be  seen  that  we  have  to  distin- 
guish between  the  following  kinds  of  connective  tissue  :  (i)  mucous 
connective  tissue,  (2)  reticular  connective  tissue,  (3)  fibrous  con- 
nective tissue,  (4)  adipose  tissue,  (5)  cartilage,  (6)  bone. 

The  fibrous  connective  tissues  are  composed  of  a  ground-sub- 
stance or  matrix  in  which  are  imbedded  the  cellular  elements  and 
two  kinds  of  connective-tissue  fibers,  namely,  white  and  elastic 
fibers.  As  the  character  of  the  fibrous  connective  tissue  depends 
largely  on  the  arrangement  of  the  fibers  and  on  the  relative  propor- 
tion of  the  white  and  elastic  fibers,  these  will  be  considered  prior  to 
a  description  of  the  several  types  of  fibrous  connective  tissue. 

White  Fibers. — White  fibrous  connective  tissue  consists  of  ex- 
ceedingly fine  homogeneous  fibrillse,  cemented  by  a  small  amount 
of  an  interfibrillar  cement  substance  into  bundles  varying  in  size.  In 
the  bundles  these  fibrillae  have  a  parallel  course,  although  the  bun- 
dles are  often  slightly  wavy.  The  fibrillae  of  white  fibrous  connective 
tissue  vary  in  size  from  0.25  to  I  //,  and  neither  branch  nor  anasto- 


THE    CONNECTIVE    TISSUES.  9! 

mose.  They  become  transparent  and  swollen  when  treated  with 
acetic  acid,  are  not  at  all  or  only  very  slowly  digested  by  pancreatin, 
and  yield  gelatin  on  boiling. 

Elastic  Fibers. — These  are  homogeneous,  highly  refractive,  dis- 
tinctly contoured  fibers,  varying  in  size  from  I  /i  to  6//,  and  in  some 
animals  are  even  larger.  They  branch  and  anastomose,  and  are  not 
cemented  into  bundles.  When  extended,  they  appear  straight ; 
when  relaxed,  they  show  broad,  bold  curves,  or  are  arranged  in 
the  form  of  a  spiral.  The  broken  ends  of  the  fibers  are  bent  in  the 
form  of  a  hook.  F.  P.  Mall  has  shown  that  elastic  fibers  are  com- 
posed of  two  distinct  substances — an  outer  delicate  sheath  which  does 
not  stain  in  magenta,  and  an  interior  substance  which  is  intensely 
colored  in  this  stain.  The  interior  substance  is  highly  refractive. 
Elastic  fibers  are  not  affected  by  acetic  acid,  but  are  readily  digested 
in  pancreatin  and  less  readily  in  pepsin.  They  yield  elastin  on 
boiling. 

Our  knowledge  concerning  the  development  of  the  connective- 


Fig.  58. — White  fibrils  and  small  bun- 
dles of  white  fibrils  from  teased  preparation 
of  a  fresh  tendon  from  the  tail  of  a  rat. 


Fig.  59. — Elastic  fibers  from  the  liga- 
mentum  nuchse  of  the  ox,  teased  fresh  ; 
X  5°°-  At  a  the  fiber  is  curved  in  a  char- 
acteristic manner. 


tissue  fibers  is  not  as  yet  conclusive  ;  two  distinct  views  are  held  at 
the  present  time.  One  group  of  observers  maintains  that  the  fibers 
are  developed  in  the  cells  of  the  embryonic  connective  tissue. 
These  cells  are  thought  to  change  into  fibrous  connective  tissue  by 
the  formation  in  their  interior  of  thread-like  structures — the  con- 
nective-tissue fibrils — a  process  which  is  always  accompanied  by 
active  nuclear  division  (Flemming,9i,  II;  Lwoff,  Reinke).  The  cells 
thus  become  polynuclear  and  considerably  lengthened,  and  the 
fibrils  gradually  increase  in  number  at  the  expense  of  the  cell-bodies, 
so  that  on  examining  the  tissue  the  fibrils  appear  to  predominate, 
and  give  the  impression  of  forming  the  ground-substance.  Ac- 
cording to  the  other  view,  the  fibers  are  at  all  times  intercellular, 
developing  in  the  ground-substance.  Mall  believes  their  develop- 
ment to  be  due  to  a  kind  of  coagulation,  certain  cells  being  held 


92  THE     TISSUES. 

responsible  for  the  formation  of  special  fluids  or  ferments  which 
bring  about  this  coagulation.  The  formation  of  the  ground-sub- 
stance in  which  the  fibers  develop  is  also  attributed  to  the  cellular 
elements.  The  intercellular  mode  of  formation  of  connective- 
tissue  fibers  would  appear  to  be  the  more  usual,  although  some  of 
them  may  have  an  intracellular  origin.  We  shall  now  discuss  the 
several  types  of  fibrous  connective  tissue. 

J.  MUCOUS  CONNECTIVE  TISSUE. 

Mucous  connective  tissue  is  a  purely  embryonal  type,  and 
scarcely  represented  in  the  adult  human  body.  It  consists  of 
branched,  anastomosing  cells  imbedded  in  a  gelatinous  ground-sub- 
stance, containing  here  and  there  white  fibers.  The  latter  as  well  as 
the  mucous  matrix  are,  directly  or  indirectly,  the  products  of  the 
-cells.  During  the  development  of  the  embryo  this  tissue  is  found  in 
large  quantities  in  the  umbilical  cord,  and  is  here  known  as  Whar- 
ton's  jelly.  It  also  occurs  in  the  embryo  in  the  cutis,  in  the  region 
of  the  semicircular  canals  of  the  cochlea,  in  the  vitreous  humor,  etc. 


2.  RETICULAR  CONNECTIVE  TISSUE. 

Reticular  connective  tissue  is  a  fibrous  connective  tissue  in  which 
the  intercellular  substance  has  disappeared.  The  tissue  is  often 
described  as  being  composed  of  anastomosing  branched  cells,  ar- 
ranged in  the  form  of  a  network  with  open  spaces.  The  obser- 
vations of  Ranvier  and  Bizzozero,  and  more  recently  those  of  Mall, 
have  shown  that  the  framework  of  reticular  tissue  is  composed  of 
very  fine  fibrils  or  bundles  of  fibrils.  These  interlace  in  all  planes 
to  form  a  most  intricate  network,  surrounding  spaces  of  varying  size 
and  shape.  According  to  F.  P.  Mall,  the  fibrils  of  reticular  tissue 
differ  chemically  from  both  the  white  and  elastic  fibers,  although  their 
composition  has  not  been  fully  determined.  Like  white  fibrous 
tissue,  reticular  tissue  is  not  digested  by  pancreatin,  but,  unlike 
white  fibrous  tissue,  it  does  not  appear  to  yield  gelatin  upon  boiling 
in  water. 

The  cells  of  reticular  connective  tissue,  which  are  flattened  and 
often  variously  branched,  lie  on  the  reticular  network,  being  often 
wrapped  about  the  bundles  of  fibrils.  Unless  they  are  removed,  the 
reticulum  has  the  appearance  of  a  network  composed  of  branched 
and  anastomosing  cells. 

Reticular  connective  tissue  is  found  in  adenoid  tissue  and  lymph - 
glands,  in  the  spleen,  and  in  the  mucous  membrane  of  the  intestinal 
canal,  and  in  these  locations  the  meshes  of  the  reticulum  are  filled  with 
lymph-cells  and  other  cellular  elements,  which,  unless  removed, 
obscure  the  reticulum.  Connective -tissue  fibrils  giving  the  same 
reaction  as  those  found  in  the  adenoid  reticulum  are  found  associ- 
ated with  white  and  elastic  fibers  in  the  liver,  kidneys,  and 


THE    CONNECTIVE    TISSUES. 


93 


lung.       In   bone-marrow  a  reticulum  is   found,  in  the  meshes   of 
which  are  the  cellular  elements  of  this  tissue. 


3.  FIBROUS  CONNECTIVE  TISSUE. 

Fibrous  connective  tissue  can  be  divided  morphologically  into 
two  groups  :  In  one  the  bundles  of  fibers  cross  and  interlace  in 
all  directions,  forming  a  network  with  meshes  of  varying  size — 
formless  or  areolar  connective  tissue.  In  the  other  the  bundles  of 
fibers  are  parallel  to  each  other,  as  in  tendon  and  many  of  the  apo- 
neuroses  and  ligaments,  or  less  regularly  arranged,  yet  very  densely 


i 

vO  \    — 


Reticulum. 


Fig.   60. — Reticular  connective  tissue  from  lymph-gland  of  man  ;  X 

preparation. 


Nucleus  of 
connec- 
tive-tis- 
sue cell. 


Blood- 
vessel. 


Brush 


woven,  as  in  fascias,  the  dura  mater,  and  the  firm,  fibrous  capsules 
of  some  of  the  organs. 

(a)  In  areolar  connective  tissue  the  bundles  of  white  fibers, 
which  vary  greatly  in  size  and  which  often  divide  and  anastomose  with 
portions  of  other  branching  bundles,  intercross  and  interlace  in  all 
directions.  If  the  bundles  of  fibers  are  numerous,  the  interlacement  is 
more  compact,  thus  forming  a  dense  areolar  connective  tissue  ;  if  less 
numerous,  the  network  is  more  open,  as  in  loose  areolar  connective 
tissue.  Elastic  fibers  are  always  found  in  areolar  connective  tissue, 
though  in  varying  quantity.  They  anastomose  to  form  a  network 
with  large,  irregular  meshes,  and  run  on  or  between  the  bundles  of 
white  fibers.  The  meshes  between  the  bundles  of  fibers,  and  the 
minute  spaces  between  the  fibrils  in  these  bundles,  are  occupied  by 
a  semifluid,  homogeneous  substance  known  as  the  ground-substance, 
or  matrix.  The  fibrous  elements  of  areolar  connective  tissue  are, 


94 


THE     TISSUES. 


therefore,  imbedded  in  this  ground-substance,  in  which  they  develop. 
In  dense  areolar  connective  tissue  the  fibrous  elements  appear  to 
have  nearly  displaced  the  ground-substance.  In  the  ground-sub- 
stance are  found  irregular,  branched  spaces, — cell-spaces, — in  which 
lie  the  cellular  elements  of  this  connective  tissue.  These  spaces 
anastomose  by  means  of  their  branches,  thus  forming  part  of  a 

system  of  spaces  and  small  chan- 

|^  ;  nels,  known  as  the  lymph  canal- 

^^4^  icular  system.  These  spaces  and 
channels  permeate  the  ground- 
substance  in  all  directions,  and 
serve  to  convey  lymph  to  the 
tissue  elements.  The  cell-spaces 
and  their  anastomosing  branches 
can  be  demonstrated  by  immers- 
ing areolar  connective  tissue 
(preferably  from  a  young  animal), 
spread  out  in  a  thin  layer,  in  a 
solution  of  silver  nitrate  ( I  fy ) 
until  the  tissue  becomes  opaque. 
If  then  the  tissue  is  exposed  to 
sunlight,  the  silver  is  reduced  in  the  ground-substance,  giving  it  a 
brown  color,  while  the  cell-spaces  remain  unstained.  The  ground- 
substance  of  areolar  connective  tissue  contains  mucin. 

The  cellular  elements  of  areolar  connective  tissue,  which,  as 
above  stated,  are  imbedded  in  the  cell-spaces,  are  either  fixed  con- 


Fig.  61. — Areolar  connective  tissue 
from  the  subcutaneous  tissue  of  a  rat. 
Elastic  fibers  not  shown. 


Fig.  62. — Cell  -  spaces  in  the  ground- 
substance  of  areolar  connective  tissue  (sub- 
cutaneous) of  a  young  rat.  Stained  in  silver 
nitrate. 


Fig.  63. — Three  connective-tissue 
cells  from  the  pia  mater  of  a  dog.  Stained 
in  methylene-blue  (intra  vitam}. 


nective-tissue  cells  or  wandering  or  migratory  cells.  The  former 
are  again  divided,  according  to  their  shape  and  structure,  into 
true  connective-tissue  cells  or  corpuscles,  granular  cells,  plasma 
cells,  and  pigment  cells. 

The  connective-tissue  cells  or  corpuscles  are  flattened,  variously 
shaped  cells  of  irregular  form,  usually  having  many  branches.     The 


THE    CONNECTIVE    TISSUES. 


95 


protoplasm  is  free  from  granules  ;  the  nucleus,  situated  in  the  thicker 
portion  of  the  cell-body  and  of  oval  shape,  shows  a  nuclear  net- 
work and  one  or  several  nucleoli.  The  cells  assume  the  shape  of 


Fig.  64.  — Two  pigment  cells  found  on  the  capsule  of  a  sympathetic  ganglion  of  a  frog. 

the  space  that  they  occupy  and  nearly  fill.  The  branches  of  neigh- 
boring cells  often  anastomose  through  the  fine  channels  uniting  the 
cell-spaces. 

Granular  cells  are  thus  named  because  in  their  protoplasm  are 
found  rather  coarse  granules  of  an  albuminous  nature  which  stain 


Bacterium  in  a 
vacuole. 


Fig.  65. — Leucocyte  of  a  frog  with  pseudopodia.     The  cell  has  included  a  bacterium 
which  is  in  process  of  digestion.     (After  Metschnikoff,  from  O.  Hertwig,  93,  II). 

readily  in  many  anilin  stains,  notably  eosin.  They  are  of  irregular 
form,  and  are  generally  found  in  the  neighborhood  of  blood-vessels. 
The  nucleus  is  relatively  large  and  of  round  or  oval  form. 


96  THE    TISSUES. 

Plasma  cells,  first  described  by  Waldeyer,  show  large  vacuoles 
in  their  protoplasm. 

Pigment  cells  are  branched  connective-tissue  cells,  in  the  proto- 
plasm of  which  are  found  brown  or  nearly  black  granules.  In  man 
they  occur  in  the  choroid  and  iris  and  in  the  dermis.  In  the  lower 
animals  they  have,  however,  a  much  wider  distribution,  and  in  the 
frog  and  other  amphibia  they  are  very  large  and  irregular.  These 
cells  have  the  power  of  withdrawing  their  processes  and,  to  a  limited 
degree,  of  changing  their  location  (dermis). 

The  wandering  or  migratory  cells  are  described  in  this  connec- 
tion not  because  they  form  one  of  the  structural  elements  of  areolar 
connective  tissue,  but  because  they  are  always  associated  with  it. 
They  are  lymph-  or  white  blood-cells,  which  have'leftthe  lymph-  or 
blood-vessels  and  have  migrated  into  the  lymph  canalicular  system. 
They  possess  ameboid  movement,  and  wander  from  place  to  place, 


Fibrils. 


Nucleus. w~- 


Fig.  66. — Fibrous  connective  tissue  (areolar)  from  the  great  omentum  of  the  rabbit ; 
X  400.     Technic  No.  17. 

and  are  the  phagocytes  of  Metschnikoff.  They  seem  to  be  intrusted 
with  the  removal  of  substances  either  superfluous  or  detrimental  to 
the  body  (as  bacteria).  These  are  either  digested  or  rendered  harm- 
less. The  wandering  cells  even  transport  substances  thus  taken  up 
to  some  other  region  of  the  body,  where  they  are  deposited. 

In  the  peritoneum  and  other  serous  membranes  the  network 
formed  by  the  fibrous  tissue  lies  in  one  plane,  and  does  not  branch 
and  intercross  in  all  directions,  as  where  areolar  tissue  is  found  in 
larger  quantity.  (Fig.  66.) 

(£)  Tendons,  aponeuroses,  and  ligaments  represent  the  densest 
variety  of  fibrous  connective  tissue,  and  are  composed  almost 
wholly  of  white  fibrous  tissue.  This  is  found  in  the  form  of  rela- 
tively large  bundles  of  white  fibrils,  having  a  parallel  or  nearly 
parallel  course.  In  tendons  these  bundles  are  known  as  primary 
tendon  bundles  or  tendon  fasciculi.  The  fibrils  of  white  fibrous  con- 


THE    CONNECTIVE    TISSUES. 


97 


nective  tissue  forming  the  fasciculi  are  cemented  together  by  an  in- 
terfibrillar  cement  substance.  Here  and  there  the  fasciculi  branch 
at  very  acute  angles  and  anastomose  with  other  fasciculi.  The  fas- 
ciculi are  grouped  into  larger  or  smaller  bundles,  the  secondary 
tendon  bundles,  which  are  surrounded  by  a  thin  layer  of  areolar  con- 
nective tissue,  and  in  part  covered  by  endothelial  cells.  Between 
the  tendon  fasciculi  there  is  found  a  ground-substance,  interfascicu- 
lar  ground-substance,  identical  with  the  ground-substance  in  areolar 
connective  tissue.  In  this  there  are  cell-spaces  occupied  by  the 
tendon  cells,  morphologically  similar  to  the  branched  cells  of  areolar 
connective  tissue.  The  tendon  cells  are  arranged  in  rows  between  the 
tendon  fasciculi.  They  have  an  irregular,  oblong  body,  containing 
a  nearly  round  or  oval  nucleus.  Two,  three,  or  even  more  wing- 


Tendon  cell. 


Tendon  fibers. 


Fig.  67. — Longitudinal  section  of  tendon  ; 


Tendon 


#       •  ~"  Tendon 

^_^if^f  fasciculus. 

Fig.    68. — Cross- section   of   secondary 
tendon  bundle  from  tail  of  a  rat. 


like  processes  (lamellae)  come  from  the  cell-body  and  pass  between 
the  tendon  fasciculi.  In  cross-section  the  tendon  cells  have  a 
stellate  shape. 

The  secondary  tendon  bundles  are  grouped  to  form  the  tendon, 
and  the  whole  is  surrounded  and  held  together  by  a  layer  of  areolar 
connective  tissue,  called  the  peritendineum.  From  this,  septa  pass  in 
between  the  secondary  tendon  bundles,  forming  the  internal  peri- 
tendineum. The  blood-  and  lymph-vessels  and  the  nerve-fibers 
reach  the  interior  of  the  tendon  through  the  external  and  internal 
peritendineum. 

The  structure  of  an  aponeurosis  and  a  ligament  is  like  that  of  a 
tendon. 

The  structure  of  a  fascia,  the  dura  mater,  and  the  more  fully 
7 


98 


THE     TISSUES. 


developed  gland  capsules,  differs  from  that  of  the  formed  connective 
tissues  above  described,  in  that  the  fasciculi  are  not  so  regularly 
arranged,  but  branch  and  anastomose  and  intercross  in  several 
planes. 

(c)  Elastic  Fibrous  Tissue. — In  certain  connective  tissues  the 
elastic  fibers  predominate  greatly  over  the  fibers  of  white  fibrous 
connective  tissue.  These  are  spoken  of  as  elastic  fibrous  tissues  and 
their  structural  peculiarities  warrant  the  making  of  a  special  sub- 
group. 

The  ligamentum  nuchse  of  the  ox  consists  almost  exclu- 
sively of  elastic  fibers,  many  of  which  attain  a  size  of  about  io//. 
The  elastic  fibers  branch  and  anastomose,  retaining,  however,  a 
generally  parallel  course.  They  are  separated  by  a  small  amount  of 
areolar  connective  tissue,  in  which  a  connective-tissue  cell  is  here 
and  there  found,  and  are  grouped  into  bundles  surrounded  by  thin 
layers  of  areolar  connective  tissue  ;  the  whole  ligament  receives  an 


- 


1 


Areolar  con- 
nective tis- 
sue. 

Nucleus  of  con- 
nective-tissue 
cell. 


Fig.  69. — Tendon  cells  from  the 
tail  of  a  raU  Stained  in  methylene- 
blue  (intra  vitani}. 


Fig.   70. —  Cross-section    of    ligamentum 
nuchae  of  ox. 


investment  of  this  tissue.  In  cross-sections  of  the  ligamentum 
nuchae,  the  larger  elastic  fibers  have  an  angular  outline  ;  the  smaller 
ones  are  more  regularly  round  or  oval.  (Fig.  70.)  In  man  the 
ligamenta  subflava,  between  the  laminae  of  adjacent  vertebrae,  are 
elastic  ligaments. 

In  certain  structures  (arteries  and  veins),  the  elastic  tissue  is 
arranged  in  the  form  of  membranes.  It  is  generally  stated  that 
such  membranes  are  composed  of  flat,  ribbon-like  fibers  or  bands  of 
elastic  tissue  arranged  in  the  form  of  a  network,  with  larger  or  smaller 
openings  ;  thus  the  term  fenestrated  membranes.  F.  P.  Mall  has 
reached  the  conclusion  that  such  membranes  are  composed  of  three 
layers — an  upper  and  a  lower  thin  transparent  layer  in  which  no 
openings  are  found  and  which  are  identical  with  the  sheaths  of 
elastic  fibers  described  by  this  observer,  and  a  central  layer,  contain- 
ing openings,  and  staining  deeply  in  magenta.  This  substance  is 
identical  with  the  central  substance  of  elastic  fibers. 


THE    CONNECTIVE    TISSUES.  99 

4.  ADIPOSE  TISSUE. 

In  certain  well-defined  regions  of  the  body  occur  typical  groups 
of  fixed  connective-tissue  cells  which  always  change  into  fat-cells  (fat 
organs, Toldt).  Connective-tissue  cells  in  various  other  portions  of  the 
body  may  also  change  into  fat-cells,  but  in  this  case  the  fat,  as  such, 
sometimes  disappears,  allowing  the  cells  to  resume  their  original  con- 
nective-tissue type,  only  again  to  appear  and  a  second  time  change  the 
character  of  the  tissue.  The  formation  of  fat  is  very  gradual.  Very 
fine  fat  globules  are  deposited  in  the  cell  ;  these  coalesce  to  form 
larger  ones,  until  finally  the  cell  is  almost  entirely  filled  with  a 
large  globule  (vid.  also  H.  Rabl,  96). 

As  the  fat  globule  grows  larger  and  ^^g^-r-;.- .Nucleus, 

larger,  the  protoplasm  of  the  cell,  to-          >'a&         ML    Protoplasm, 
gether  with  its  nucleus,  is  crowded  to         /«  Bj\ 

the  periphery.     The  protoplasm  then        •  IP  Fat  drop, 

appears  as  a  thin  layer  just  within  the  WP     Cell-membrane- 

clear  cellular  membrane.   The  nucleus 

becomes  flattened  by  pressure,  until  Fig.  71.— Scheme  of  a  fat-cell, 
in  profile  view  it  has  the  appearance 

of  a  long,  flat  body.  In  regions  in  which  large  masses  of  fat- 
cells  are  developed,  they  are  seen  to  be  gathered  into  rounded 
groups  of  various  sizes  (fat  lobules)  separated  by  strands  of  con- 
nective tissue.  Numerous  blood-vessels  are  imbedded  in  this  con- 
nective tissue,  penetrating  into  the  lobules  and  there  breaking  up 
into  a  rich  capillary  network. 

Microscopically,  fat  is  easily  recognized  by  its  peculiar  glistening 
appearance  (by  direct  light).  It  has  a  specific  reaction  to  certain 
reagents.  It  becomes  black  on  treatment  with  osmic  acid,  and  is 
stained  red  by  Sudan  III. 

5.  CARTILAGE. 

The  simplest  type  is  hyaline  cartilage,  so  named  because  of  its 
homogeneous  and  transparent  ground-substance.  Cartilage  cells,  as 
such,  are  of  various  shapes,  and  have  no  typical  appearance.  They 
are  usually  scattered  irregularly  throughout  the  matrix,  but  are 
often  arranged  in  groups  of  two,  three,  four,  or  even  more  cells. 
At  the  periphery  of  cartilage,  either  where  it  borders  upon  a  cavity 
(articular  cavity)  or  where  it  joins  the  perichondrium,  the  cells  are 
arranged  in  several  rows-  parallel  to  the  surface  of  the  tissue. 
Cartilage  cells  often  contain  glycogen,  either  in  the  form  of  drops 
or  diffused  throughout  their  protoplasm. 

The  matrix  of  cartilage  is  the  product  of  the  cell.  It  is  not 
present  in  the  so-called  precartilagc  (embryonal  cartilage),  in  which 
the  cells  lie  close  together  with  their  membranes  touching.  The 
ground-substance  is  gradually  formed  as  follows  :  The  membranes 
of  the  cells  thicken,  pressing  the  cells  apart.  Inside  of  the  mem- 
branes the  cells  divide,  and  each  resulting  cell  again  forms  a  mem- 


100 


THE     TISSUES. 


brane.  Membranes  of  the  mother  cells  fuse  to  form  the  ground- 
substance  or  matrix.  The  newly  created  membranes  of  the  daughter 
cells  pass  through  the  same  process,  and  fuse  not  only  with  each 


Matrix. 


Cartilage  cell.  —-j£& 


Fig.  72. — Hyaline  cartilage  (costal  cartilage  of  the  ox).  Alcohol  preparation  ; 
X  300.  The  cells  are  seen  inclosed  in  their  capsules.  In  the  figure  a  are  represented 
frequent  but  by  no  means  characteristic  radiate  structures. 


other,  but  also  with  the  matrix.  The  cartilage  thus  gradually  as- 
sumes the  appearance  of  its  adult  stage.  The  youngest  cells  also 
possess  membranes  which  separate  them  from  the  ground-sub- 
stance. These  are  known  as  the  capsules.  The  spaces  occupied 
by  the  cells  are  called  lacunce. 


Fig.  73. — From  a  section  through  the  cranial  cartilage  of  a  squid  (after  M.  Fiirbringer, 

from  Bergh). 

From  the  description  just  given  it  would  seem  that  cartilage 
grows  only  by  intussusception,  but  as  a  matter  of  fact  an  apposi- 
tional  growth,  although  in  a  lesser  degree,  also  takes  place.  It 


THE    CONNECTIVE    TISSUES. 


101 


occurs  where  the  cartilage  borders  upon  its  connective-tissue  sheath 
or  perichondrium,  a  vascular,  fibrous-tissue  membrane  composed  of 
white  and  elastic  fibers,  which  covers  the  cartilage  except  where 
it  forms  a  joint  surface.  The  relations  of  the  cartilage  and  peri- 
chondrium are  extremely  intimate.  Fibers  are  seen  passing  from 
the  perichondrium  into  the  cartilaginous  matrix,  and  the  connective- 
tissue  cells  appear  to  change  directly  into  cartilage-cells. 


White  fibrous  connec- 
tive tissue. 


White  fibrocartilage. 


|,  I  Insertion  of  liga- 
mentum  teres. 


/Hyaline  cartilage. 


74- — Insertion  of  the  ligamentum  teres  into  the  head  of  the  femur.     Longitudinal 
section  ;   X  650. 


It  is  an  interesting  fact  that  the  cartilage  of  certain  invertebrate 
animals,  the  cephalopoda,  shows  cells  with  anastomosing  processes. 
(Fig-  73-)  In  tm's  case  the  cartilage -cell  is  similar  to  a  bone-cell, 
thus  theoretically  allowing  of  the  possibility  of  the  metamorphosis 
of  the  elements  of  cartilage  into  those  of  bone  (M.  Fiirbringer). 

Hyaline  cartilage  occurs  as  articular  cartilage,  covering  joint 
surfaces,  as  costal  cartilage  and  in  the  nose,  larynx,  trachea,  and 


102 


THE     TISSUES. 


bronchi.  All  bones  except  those  of  the  vault  of  the  skull  and  the 
majority  of  the  bones  of  the  face  are  preformed  in  hyaline  cartilage. 

In  white  fibrocartilage  (Fig.  74)  there  are  from  the  beginning, 
even  in  precartilage,  fibrous  strands  in  the  ground-substance.  They 
preponderate  over  the  matrix  and,  as  a  rule,  have  a  parallel  direc- 
tion. White  fibrocartilage  is  found  in  the  intervertebral  and  inter- 
articular  disks,  the  symphysis  pubis,  and  in  the  insertion  of  the 
ligamentum  teres  ;  it  deepens  the  cavity  of  ball-and-socket  joints, 
and  lines  the  tendon  grooves. 

In  some  places  elastic  fibers  are  found  imbedded  in  hyaline  car- 
tilage— -fibro-elastic  cartilage.  The  elastic  fibers  send  off  at  acute 
angles  finer  or  coarser  threads  which  interlace  to  form  a  delicate  or 


^--Cartilage-cell. 


JLV--0 


—  Elastic  fibers. 


Fig.  75- — Elastic  cartilage  from  the  external  ear  of  man  ;   X  7^o.     Technic  No.  149. 
a,  Fine  elastic  network  in  the  immediate  neighborhood  of  a  capsule. 


dense  network  which  permeates  the  hyaline  matrix  (Fig.  75),  pass- 
ing over  into  the  corresponding  elements  of  the  perichondrium. 
Elastic  cartilage  is  found  in  the  external  ear,  the  cartilage  of  the 
Eustachian  tube,  the  epiglottis,  a  portion  of  the  arytenoid  cartilages, 
and  the  cartilages  of  Wrisberg  and  Santorini. 

The  hyaline  ground-substance  of  all  three  forms  of  cartilage, 
together  with  the  contained  fibers,  may  undergo  calcification,  es- 
pecially in  old  age.  This  renders  the  tissue  brittle  and  easily 
broken. 

The  nutrition  of  cartilage  is  partially  supplied  by  blood-vessels 
in  the  matrix,  which,  however,  are  not  numerous.  Very  fine  lymph- 


THE    CONNECTIVE    TISSUES.  1 03 

canals  are  probably  also  present  in  the  matrix,  uniting  the  lacunae, 
through  which  lymph  plasma  circulates  (vid.  researches  of  Flesch, 
Budge,  Solger  (88,  II),  van  der  Stricht  (87),  etc.). 

To  obtain  chondrin,  a  piece  of  cartilage  matrix  is  placed  in  a 
tube  containing  water.  This  is  hermetically  closed  and  heated  to 
120°  C,  after  which  it  is  opened  and  the  fluid  filtered  and  treated 
with  alcohol.  A  precipitate  of  chondrin  is  the  result.  This  sub- 
stance is  insoluble  in  cold  water,  alcohol,  and  ether,  but  soluble  in 
hot  water,  although,  on  cooling,  it  gelatinizes.  In  contrast  to  gel- 
atin, chondrin  is  precipitated  by  acetic  acid.  This  precipitate  does 
not  redissolve  in  an  excess  of  this  acid  but  disappears  in  an  excess 
of  certain  mineral  acids. 


6.  BONE. 

.  (a)  Structure  of  Bone. — Bone  nearly  always  develops  from  a 
connective-tissue  foundation,  even  where  it  occurs  in  places  formerly 
occupied  by  cartilage. 

The  inorganic  substance  of  bone  is  deposited  in  or  between  the 
fibers  of  connective  tissue,  while  the  cells  of  the  latter  are  trans- 
formed into  bone-cells. 

As  in  connective  tissue,  so  also  in  bone,  the  ground-substance 
is  fibrous.  Between  the  fibers  remain  uncalcified  cells,  bone-cells, 
each  of  which  rests  in  a  cavity  of  the  matrix — lacuna. 

Primarily,  bone  consists  of  a  single  thin  lamella,  its  later  com- 
plicated structure  being  produced  by  the  formation  of  new  lamellae 
in  apposition  to  the  first.  During  its  development  the  bone  becomes 
vascularized,  and  the  vessels  are  inclosed  in  especially  formed  canals 
known  as  vascular  or  Haversian  canals.^ 

The  bone-cells  have  processes  that  probably  anastomose,  and 
that  lie  in  special  canals  known  as  bone  canaliculi.  Whether,  in 
man,  all  the  processes  of  bone-cells  anastomose  is  still  an  open 
question. 

The  appearance  presented  by  a  transverse  section  of  the  shaft 
of  a  long  bone  is  as  follows  :  In  the  center  is  a  large  marrow  cavity, 
and  at  the  periphery  the  bone  is  covered  by  a  dense  connective- 
tissue  membrane,  the  periosteum.  In  the  new-born  and  in  young  in- 
dividuals the  periosteum  is  composed  of  three  layers — an  outer  layer, 
consisting  mainly  of  rather  coarse,  white  fibrous-tissue  bundles  that 
blend  with  the  surrounding  connective  tissue  ;  a  middle  fibro-elastic 
layer,  in  which  the  elastic  tissue  greatly  predominates  ;  and  an  inner 
layer,  the  osteogenetic  layer,  vascular  and  rich  in  cellular  elements, 
containing  only  a  few  smaller  bundles  of  white  fibrous  tissue.  In 
the  adult  the  osteogenetic  layer  has  practically  disappeared,  leav- 
ing only  here  and  there  a  few  of  the  cells  of  the  layer,  while 
the  fibro-elastic  layer  is  correspondingly  thicker  (Schulz,  96).  A 
large  number  of  Haversian  canals  containing  blood-vessels,  seen 
mostly  in  transverse  section,  are  found  in  compact  bone-substance. 


104 


THE     TISSUES. 


Lamellae  of  bone  are  plainly  visible  throughout  the  ground-sub- 
stance, and  are  arranged  in  the  following  general  systems  : 

First,  there  is  a  set  of  bone  lamellae  running  parallel  to  the  ex- 
ternal surface  of  the  bone,  while  another  set  is  similarly  arranged 
around  the  marrow  cavity.  These  are  the  so-called  fundamental, 
or  outer  and  inner  circumferential  lamellce  (known  also  as  periosteal 
and  marrow  lamellce).  Around  the  Haversian  canals  are  the  con- 
centrically arranged  lamellae,  forming  systems  of  Haversian  or  con- 
centric lamellce.  Besides  the  systems  already  mentioned,  there  are 
found  interstitial  or  ground  lamellce  wedged  in  between  the  Haversian 


Fig.  76. —  Longitudinal  section 
through  a  lamellar  system. 


Figs.  77  and  78. — Lamellae  seen  from  the  surface  ; 
X4°o  (after  v.  Ebner  75). 


a,  Primitive   fibrils    and   fibril-bundles ;    c,  bone-corpuscles  with  bone-cells ;    </,  bone 

canaliculi. 


or  concentric  systems  of  lamellae.     Some  authors  group  the  inter- 
stitial lamellae  with  the  systems  of  fundamental  lamellae. 

Lying  scattered  between  the  lamellae  are  found  spaces  known  as 
bone  corpuscles  (Virchow)  or  lacunce.  These  are  present  in  all  the 
lamellar  systems.  It  is  very  probable  that  all  the  lacunae  are  in 
more  or  less  direct  communication  with  each  other  by  means  of  fine 
canals  called  canaliculi (i .  i  p  to  1.8  //  in  diameter).  It  can  be  demon- 
strated without  difficulty  that  the  lacunae  of  a  single  lamellar  sys- 
tem communicate  not  only  with  each  other,  but  also  with  those  of 


THE    CONNECTIVE   TISSUES. 


105 


adjacent  systems.  In  the  lamellae  adjoining  the  periosteum  and  mar- 
row cavity  the  canaliculi  end  respectively  in  the  subperiosteal  tissue 
and  in  the  marrow  cavity.  The  canaliculi  of  the  Haversian  lamellae 
empty  into  the  Haversian  canals. 


-  -  - 

•-       :-    '  .    —  —  -.        -• 


- 


>   Outer  circum- 
ferential 
lamellae. 


;  , 

^    ,  *  '        \     *      '    } 

^ ,/x<    /  — -      •>rji/ 


<*    / Haversian  or 

concentric 
lamellae. 


-Haversian 
canal. 


'     '         •'   <    -    v    ^ 

v1  D  >  ,     v 


%     ,      .  •          '-«.-'        ,  •;».  "       ••   v ;    •         •  • 

wM    '  -'  :Y:  X  *?*&£  £  *  -  '•  ***C 

v*  ^r/^  ^N  '/  ^  A  >  ^  ^^' '  -VK^ 

'~~'\ "  1  ^ ^.- r—^^v''*.. 

•>  ^    i»  -^  * 


Interstitial 
lamellae. 


Inner  circum- 
ferential 
lamellae. 


Fig.  79. — Segment  of  a  transversely  ground  section  from  the  shaft  of  a  long  bone,  show- 
ing all  the  lamellar  systems.     Metacarpus  of  man  ;   X  56-     Technic  No.  152. 


The  lamellae  of  bone  are  composed  of  fine  white  fibrous-tissue 
fibrils,  embedded  in  a  ground-substance,  in  which  they  are  arranged 
in  layers,  superimposed  in  such  a  way  that  the  fibrils  in  the  several 
layers  cross  at  about  a  right  angle,  forming  an  angle  of  45°  with 


IO6  THE     TISSUES. 

the  long  axis  of  the  Haversian  canal.  It  is  as  yet  undecided 
whether  the  mineral  salts  (phosphate  and  carbonate  of  lime,  sodium 
chlorid,  magnesium  salts,  etc.)  are  deposited  in  the  ground-substance 
(v.  Ebner)  or  in  the  fibrillae  (Kolliker).  The  lacunse  ( 1 3  fj.  to  31  /j. 
long,  6  IJL  to  157^  wide,  and  4  //  to  9  JJL  thick)  have,  in  common  with  the 
canaliculi,  walls  which  present  a  greater  resistance  to  the  action  of 
strong  acids  than  the  rest  of  the  solid  bone-substance.  In  each 
lacuna  there  is  found  a  bone-cell,  the  nucleated  body  of  which 
practically  fills  the  lacuna,  while  its  processes  extend  out  into  the 
canaliculi. 

The  Haversian  canals  contain  blood-vessels,  either  an  artery  or 
a  vein  or  both.  Between  the  vessels  and  the  walls  of  the  canals 
are  perivascular  spaces  bounded  by  endothelial  cells,  resting  on  the 
adventitious  coats  of  the  vessels  and  the  sides  of  the  canals.  Into 
these  spaces  empty  the  canaliculi  of  the  Haversian  system.  Lymph- 
spaces  beneath  the  periosteum  and  at  the  periphery  of  the  marrow 


Lacuna.  " 
Canaliculi.  - 


Haversian  canal. 


Fig.  80. — Portion  of  a  transversely  ground  disc  from  the  shaft  of  a  human  femur ; 
X  400.     Technic  No.  154. 


cavity  communicate  directly  with  the  canaliculi  of  the  circumferen- 
tial systems. 

All  the  lacunae  and  canaliculi  should  be  thought  of  as  filled  by 
lymph  plasma  which  circulates  throughout,  bathing  the  bone-cells 
and  their  processes.  The  formed  elements  of  the  lymph  are  prob- 
ably too  large  to  force  their  way  through  the  very  small  canaliculi. 
The  plasma  current  probably  flows  from  the  periosteal  and  marrow 
regions  toward  the  Haversian  canals. 

Between  the  lamellae  are  bundles  of  fibers  (some  of  which  are 
calcified),  which  can  be  demonstrated  by  heating  the  bone,  or  in  de- 
calcified preparations  on  staining  by  certain  methods.  These  are  the 
so-called  ffiers  of  Sharpey  ;  in  the  adult  they  contain  elastic  fibers. 

In  the  circumferential  lamellae  are  found  canals,  not  surrounded 
by  concentric  lamellae,  which  convey  blood-vessels  from  the  perios- 
teum to  the  Haversian  canals.  These  are  called  Volkmanris  canals. 

The  structure  of  bone-marrow  will  be  discussed  with  the  blood- 
forming  organs. 


THE    CONNECTIVE    TISSUES.  IO/ 

(/;)  Development  of  Bone. — Nearly  all  the  bones  of  the  adult 
body  are,  in  the  earlier  stages  of  embryonic  life,  preformed  in  embry- 
onic cartilage.  As  development  proceeds,  this  embryonic  cartilage 
assumes  the  character  of  hyaline  cartilage,  its  cells  becoming  vesic- 
ular, and  probably  disappearing.  In  the  matrix,  however,  there 
are  formed  spaces  that  are  soon  occupied  by  cells  and  vessels  which 
grow  in  from  a  fibrous-tissue  membrane  (the  future  periosteum)  sur- 
rounding the  cartilage  fundaments  of  the  bones.  These  cells  deposit 
a  bone  matrix  in  the  cartilage  spaces.  Bone  developed  in  this  man- 
ner is  known  as  endocJiondral  or  intracartilaginous  bone.  In  certain 
bones — namely,  those  of  the  vault  of  the  skull  and  nearly  all  the 
bones  of  the  face — there  is  no  preformation  in  cartilage,  these  bones 
being  developed  from  a  connective -tissue  foundation.  They  are 
known  as  intramenibranoiis  bones.  As  will  become  evident  upon 
further  discussion  of  the  subject,  the  formation  of  fibrous-tissue 
bone  (intramembranous)  is  not  confined  to  bones  not  preformed  in 
cartilage.  In  bones  preformed  in  cartilage,  fibrous-tissue  bone  de- 
velops from  the  connective-tissue  membrane  surrounding  the  carti- 
lage fundaments,  the  two  types  of  bone-development  going  on  simul- 
taneously in  such  bones.  Attention  may  further  be  drawn  to  the 
fact  that  nearly  all  endochondral  bone  is  absorbed,  so  that  the 
greater  portion  of  all  adult  bone,  even  that  preformed  in  cartilage, 
is  developed  from  a  foundation  of  fibrous  tissue.  The  two  modes 
of  ossification — endochondral  or  intracartilaginous  and  intramem- 
branous— even  though  appearing  simultaneously  in  the  majority  of 
bones,  will,  for  the  sake  of  clearness,  be  discussed  separately. 

i .  Endochondral  Bone-development. — The  cartilage  that  forms 
the  fundaments  of  the  bones  preformed  in  cartilage  has  at  first  the 
appearance  of  embryonic  cartilage,  consisting  largely  of  cells  with 
a  small  amount  of  intercellular  matrix.  These  fundaments  are  sur- 
rounded by  a  fibrocellular  membrane — the  perichondrium.  Ossifi- 
cation is  initiated  by  certain  structural  changes  in  the  embryonic 
cartilage,  in  one  or  several  circumscribed  areas,  known  as  centers  of 
ossification.  In  the  long  bones  a  center  of  ossification  appears  in  the 
middle  of  the  future  diaphysis.  In  this  region  the  intercellular 
matrix  increases  in  amount  and  the  cells  in  size  ;  thus  the  embry- 
onic cartilage  assumes  the  character  of  hyaline  cartilage.  This  is 
followed  by  a  further  increase  in  the  size  of  the  cartilage-cells,  at 
the  expense  of  the  thinner  partitions  of  matrix  separating  neighbor- 
ing cells,  while  at  the  same  time  lime  granules  are  deposited  in  the 
matrix  remaining.  During  this  stage  the  cells  appear  first  vesicu- 
lar, distending  their  capsules,  then  shrunken,  only  partly  filling  the 
enlarged  lacunae.  They  stain  less  deeply,  and  their  nuclei  show 
degenerative  changes.  The  center  of  ossification,  in- the  middle  of 
which  these  changes  are  most  pronounced,  is  surrounded  by  a  zone 
in  which  these  structural  changes  are  not  so  far  advanced  and  which 
has  the  appearance  at  its  periphery  of  hyaline  cartilage. 

Simultaneously  with  these  changes  in  the  cartilage,  a  thin  layer 


io8 


THE     TISSUES. 


of  bone  is  deposited  by  the  perichondrium  (in  a  manner  to  be 
described  under  the  head  of  intramembranous  bone-development) 
and  the  perichondrium  becomes  the  periosteum.  This  in  the  mean- 
time has  differentiated  into  two  layers — an  outer,  consisting  largely 
of  fibrous  tissue  with  few  cellular  elements,  and  an  inner,  the 
osteogenetic  layer,  vascular  and  rich  in  cellular  elements  and  con- 
taining few  fibrous-tissue  fibers. 

Ossification  in   the  cartilage  begins  after  the    above-described 


Vesicular  cartilage- 
cells. 


Primary  periosteal 
la      " 


bone  lamella. 
-•Periosteal  bud. 


Periosteum. 


Unaltered  hyaline 
cartilage. 


Fig.  81. — Longitudinal  section  through  a  long  bone  (phalanx)  of  a  lizard  embryo. 
The  primary  bone  lamella  originating  from  the  periosteum  is  broken  through  by  the  peri- 
osteal bud.  Connected  with  the  bud  is  a  periosteal  blood-vessel  containing  red  blood- 
corpuscles. 

structural  changes  have  taken  place  at  the  center  of  ossifica- 
tion. Its  commencement  is  marked  by  a  growing  into  the  cartilage 
of  one  or  several  buds  or  tufts  of  tissue  derived  principally  from 
the  osteogenetic  layer  of  the  periosteum.  As  the  periosteal  buds 
grow  into  the  cartilage,  some  of  the  septa  of  matrix  separating  the 
altered  cartilage-cells  disappear,  and  the  cells  become  free  and 
probably  degenerate.  In  this  way  the  cartilage  at  the  center  of  ossi- 


THE    CONNECTIVE    TISSUES. 


109 


fication  becomes  hollowed  out,  and  there  are  formed  irregular  anas- 
tomosing spaces,  primary  marrow  spaces,  separated  by  partitions  or 
trabeculae  of  calcified  cartilage  matrix.  Into  these  primary  mar- 
row spaces  grow  the  periosteal  buds,  consisting  of  small  blood- 
vessels, cells,  and  some  few  connective-tissue  fibers,  forming  embry- 
onic marrow  tissue.  Some  of  the  cells  which  have  thus  grown  into 


—  Groove  of 
ossification. 


Periosteum. 


Periosteal  bone 

lamella. 

Primary  marrow 
spaces. 


Fig.  82. — Longitudinal  section  of  the  proximal  end  of  a  long  bone  (sheep  embryo)  ; 

X30- 

the  primary  marrow  spaces  arrange  themselves  in  layers  on  the 
trabeculae  of  calcified  matrix,  which  they  envelop  with  a  layer  of 
osseous  matrix  formed  by  them.  The  cells  thus  engaged  in  the 
formation  of  osseous  tissue  are  known  as  osteoblasts. 

Ossification  proceeds  from  the  center  of  ossification  toward  the 


no 


THE     TISSUES. 


extremities  of  the  diaphysis  (in  a  long  bone),  and  is  always  preceded, 
as  at  the  center  of  ossification,  by  the  characteristic  structural 
changes  above  described.  Beginning  at  the  center  of  ossification  and 
proceeding  toward  either  extremity  of  the  diaphysis,  the  enlarged  and 
vesicular  cartilage-cells  will  be  observed  to  be  arranged  in  quite  reg- 
ular columns,  separated  by  septa  or  tra- 
beculae  of  calcified  cartilage  matrix.  The 
cells  thus  arranged  in  columns  show  the 
degenerative  changes  above  described. 
They  are  shrunken  and  flattened,  and 
their  nuclei,  when  seen,  stain  less  deeply 
than  the  nuclei  of  normal  cartilage-cells. 
Beyond  this  zone  of  columns  of  altered 
cartilage-cells  are  found  smaller  or  larger 
groups  of  less  changed  cartilage-cells, 
and  beyond  this  zone,  hyaline  cartilage. 
The  arrangement  of  the  cartilage- 
cells  in  the  columns  above  mentioned  is, 
according  to  Schiefferdecker,  mainly  due 
to  two  factors  —  the  current  of  lymph 
plasma  which  flows  from  the  center  of 
ossification  toward  the  two  extremities  of 
the  cartilage  fundament,  and  the  mutual 
pressure  exerted  by  the  groups  of  carti- 
lage-cells in  their  growth  and  prolifera- 
tion. Ossification  proceeds  from  the  cen- 
ter of  the  diaphysis  toward  its  two  ex- 
tremities by  a  growth  of  osteoblasts  and 
small  vessels  into  the  columns  of  carti- 
lage-cells. Here,  also,  these  degenerate, 
leaving  in  their  stead  irregular,  oblong, 
anastomosing  spaces,  separated  by  septa 
and  trabeculae  of  calcified  cartilage  ma- 
trix on  which  the  osteoblasts  arrange 
themselves  in  layers,  and  which  they 
envelop  in  osseous  tissue.  In  a  longi- 
tudinal section  of  a  long  bone,  preformed 
in  cartilage,  the  various  steps  of  endo- 
chondral  bone-development  may,  there- 
fore, be  observed  by  viewing  the  prepa- 
ration from  either  end  to  the  center  of  the 
diaphysis,  as  may  be  seen  in  figures  82, 
83.  The  former  represents  the  appear- 
ance as  seen  under  low  magnification,  the  latter  a  small  portion  of 
such  a  section  from  the  area  of  ossification,  more  highly  magnified. 
Adjoining  the  primary  marrow  spaces  is  vesicular  cartilage 
and  columns  and  groups  of  cartilage-cells  and  finally  hyaline  car- 
tilage. 


Fig.  83. — Longitudinal  sec- 
tion through  area  of  ossification 
from  long  bone  of  human  em- 
bryo. 


THE    CONNECTIVE    TISSUES.  I  I  I 

In  the  upper  portion  of  figure  83  is  observed  a  zone  composed 
of  groups  of  cartilage-cells,  adjoining  this  a  zone  composed  of 
columns  of  vesicular  and  shrunken  cartilage-cells,  the  nuclei  of  which 
are  indistinctly  seen.  These  columns  are  separated  by  septa  and 
trabeculae  of  calcified  matrix.  This  zone  is  followed  by  one  in 
which  the  cartilage-cells  have  disappeared,  leaving  spaces  into 
which  the  osteoblasts  and  small  blood-vessels  have  grown.  In  cer- 
tain parts  of  the  figure,  the  osteoblasts  are  arranged  in  a  layer  on 
the  trabeculae  of  calcified  cartilage,  some  of  which  are  enveloped 
in  a  layer  of  osseous  matrix,  less  deeply  shaded  than  the  darker  car- 
tilage remnants. 

As  the  development  of  endochondral  bone  proceeds  from  the 
center  of  ossification  toward  the  extremities  of  the  diaphysis  in  the 
manner  described,  the  primary  marrow  spaces  at  the  center  of  ossi- 
fication are  enlarged,  a  result  of  an  absorption  of  many  of  the  smaller 
osseous  trabeculae  and  the  remnants  of  calcified  cartilage  matrix 
enclosed  by  them.  In  this  process  are  concerned  certain  large 
and,  for  the  most  part,  polynuclear  cells,  which  are  differentiated 
from  the  embryonic  marrow.  These  are  the  osteoclasts  (bone  break- 
ers) of  Kolliker  (73).  They  are  43  //  to  91  p  long  and  30  ju.  to  40 // 
broad,  and  have  the  function  of  absorbing  the  bone.  The  spaces 
which  they  hollow  out  during  the  beginning  of  the  process  appear 
as  small  cavities  or  indentations,  containing  osteoclasts  either  single 
or  in  groups,  and  are  known  as  Howship's  lacunce.  All  bone 
absorption  goes  hand  in  hand  with  their  appearance.  At  the  same 
time,  the  osseous  trabeculae  not  absorbed  become  thickened  by  a 
deposition  of  new  layers  of  osseous  tissue  (by  osteoblasts),  during 
which  process  some  of  the  osteoblasts  are  enclosed  in  the  newly 
formed  bone  and  are  thus  converted  into  bone-cells.  In  this  way 
there  is  formed  at  the  center  of  ossification  a  primary  or  embryonic 
spongy  or  cancellous  bone,  surrounding  secondary  marrow  spaces  or 
Havcrsian  spaces,  filled  with  embryonic  marrow.  This  process  of 
the  formation  of  embryonic  cancellous  bone  follows  the  primary 
ossification  from  the  center  of  ossification  toward  the  extremities  of 
the  diaphysis.  It  should  be  further  stated,  that  long  before  the 
developing  bone  has  attained  its  full  size — indeed,  before  the  end  of 
embryonic  life — the  embryonic  cancellous  bone  is  also  absorbed 
through  the  agency  of  osteoclasts.  The  Haversian  spaces  are  thus 
converted  into  one  large  cavity,  which  forms  a  portion  of  the  future 
marrow  cavity  of  the  shaft  of  the  fully  developed  bone.  The 
absorption  of  the  embryonic  cancellous  bone  begins  at  the  center 
of  ossification  and  extends  toward  the  ends  of  the  diaphysis. 

Some  time  after  the  beginning  of  the  process  of  bone  develop- 
ment at  the  center  of  ossification  of  the  diaphysis,  centers  of 
ossification  appear  in  the  epiphyses,  the  manner  of  the  develop- 
ment of  bone  being  here  the  same  as  in  the  diaphysis.  Several 
periosteal  buds  grow  into  each  center  of  ossification,  filling  the 
irregular  spaces  formed  by  the  breaking  down  of  the  degener- 


I  I  2  THE     TISSUES. 

ated  cartilage-cells.  Osteoblasts  are  arranged  in  rows  on  the 
trabeculae  of  cartilage  thus  formed,  which  they  envelop  in  osseous 
tissue.  As  development  proceeds,  the  primary  osseous  tissue  is 
converted  into  embryonic  cancellous  bone  as  above  described. 

In  the  development  of  the  epiphyses,  as  in  the  development  of 
the  smaller  irregular  bones,  the  formation  of  bone  proceeds  from 
the  center  or  centers  of  ossification  in  all  directions,  and  not  only 
in  a  direction  parallel  to  the  long  axis  of  the  bone  as  described  for 
the  diaphysis.  The  epiphyses  grow,  therefore,  in  thickness  as  well 
as  in  length,  by  endochondral  bone-development. 

There  remains  between  the  osseous  tissue  developed  in  the  dia- 
physis and  that  in  the  epiphyses,  at  each  end  of  the  diaphysis,  a  zone 
of  hyaline  cartilage  in  which  ossification  is  for  a  long  time  delayed  ; 
this  is  to  permit  the  longitudinal  growth  of  the  bone.  These  layers  of 
cartilage  constitute  the  epiphyseal  cartilages.  Here  the  periosteum 
(perichondrium)  is  thickened  and  forms  a  raised  ring  around  the 
cartilage.  As  it  penetrates  some  distance  into  the  substance  of  the 
cartilage,  the  latter  is  correspondingly  indented.  (Fig.  82.)  The  im- 
pression thus  formed  appears  in  a  longitudinal  section  of  the  bone 
as  an  indentation, — the  ossification  groove  (encoche  d' ossification, 
Ranvier,  89).  That  portion  of  the  perichondrium  filling  the  latter 
is  called  the  ossification  ridge.  The  relation  of  the  elements  of  the 
perichondrium  to  the  cartilage  in  the  region  of  the  groove  just 
described  is  an  extremely  intimate  one,  both  tissues,  perichondrium 
and  cartilage,  merging  into  each  other  almost  imperceptibly.  It  is 
a  generally  accepted  theory  that  so  long  as  the  longitudinal  growth 
of  the  bone  persists,  new  cartilage  is  constantly  formed  at  these 
points  by  the  perichondrium.  In  the  further  production  of  bone 
this  newly  developed  cartilage  passes  through  the  preliminary 
changes  necessary  before  the  actual  commencement  of  ossification 
— i.  e.,  it  goes  through  the  .stages  of  vesicular  cartilage  and  the 
formation  of  columns  of  cartilage-cells,  in  place  of  which,  later,  the 
osteoblasts  and  primary  marrow  cavities  develop. 

By  the  development  of  new  cartilage  elements  from  the  encoche 
the  longitudinal  growth  of  the  bone  is  made  possible ;  at  the  same 
time,  those  portions  of  the  cartilage  thus  used  up  in  the  process  of 
ossification  are  immediately  replaced.  (Fig.  84.) 

The  following  brief  summary  of  the  several  stages  of  endochon- 
dral bone-development  may  be  of  service  to  the  student  : 

1.  The    embryonic    cartilage    develops    into  hyaline   cartilage, 
beginning  at  the  centers  of  ossification. 

2.  The  cartilage-cells  enlarge  and  become  vesicular.     In   the 
diaphysis  of  long  bones  such   cells  are   arranged   in  quite   regular 
columns,  while  in  the  epiphyses  and  irregular  bones  this  arrange- 
ment is  not  so  apparent. 

3.  Calcification  of  the  matrix  ensues  ;  the  cartilage-cells  disap- 
pear (degenerate)  ;  primary  marrow  spaces  develop. 

4.  Ingrowth  of  periosteal  buds.     The  osteoblasts  are  arranged 


THE    CONNECTIVE    TISSUES.  I  I  3 

in  layers  on  the  trabeculse  of  calcified  cartilage,  which  they  envelop 
with  osseous  tissue. 

5.  Osteoclasts    cause    the  absorption   of  many  of   the  smaller 
osseous   trabeculae  ;  others   become  thickened  by  a  deposition  of 
new  layers  of  osseous  tissue.     Osteoblasts   are  enclosed  in   bone- 
tissue  and  become  bone-cells.      In  this  way  there  is  formed  embry- 
onic cancellous  bone,  bounding  Haversian  spaces  inclosing  embry- 
onic marrow. 

6.  In  the  diaphysis,  the  greater  portion  of  the  embryonic  can- 
cellous bone  is  also  absorbed  (by  osteoclasts)  ;  the  Haversian  spaces 
unite  to  form  a  part  of  the  marrow  space  of  the  shaft  of  the  bone. 

2.  Intramembranous  Bone. — This,  the  simpler  type  of  ossifi- 
cation, occurs  in  bone  developed  from  a  connective-tissue  founda- 
tion, and  is  exemplified  in  the  formation  of  the  bones  of  the 


Ossification 
ridge. 
Epiphysea 
cartilage. - 


Fig.  84. — Longitudinal  section  through  epiphysis  of  arm  bone  of  sheep  embryo  ;   X  12. 
<z,  b,  Primary  marrow  spaces  and  bone  lamellae  of  the  diaphysis. 

cranial  vault  and  the  greater  number  of  the  bones  of  the  face,  and 
also  in  bone  developed  from  the  periosteum  (perichondrium)  sur- 
rounding the  cartilage  fundaments  of  endochondral  bone.  All 
fibrous-tissue  bone  is  developed  in  the  same  way. 

The  intramembranous  bone-development  begins  by  an  approxi- 
mation and  more  regular  arrangement  of  the  osteoblasts  of  the 
osteogenetic  layer  of  the  periosteum  about  small  fibrous-tissue 
bundles.  The  osteoblasts  then  become  engaged  in  the  formation 
of  the  osseous  tissue  which  envelops  the  fibrous-tissue  bundles. 
In  this  way  a  spongy  bone  with  large  meshes  is  formed,  consisting 
of  irregular  osseous  trabeculae,  surrounding  primary  marrow  spaces. 
These  latter  are  filled  by  embryonic  marrow  and  blood-vessels  de- 
veloped from  the  tissue  elements  of  the  periosteum  not  engaged  in 
the  formation  of  bone. 


114  THE     TISSUES. 

Intramembranous  bone  first  appears  in  the  form  of  a  thin  lamella 
of  bone,  which  increases  in  size  and  thickness  by  the  formation  of 
trabeculae  about  the  edges  and  surfaces  of  that  previously  formed 
and  in  the  manner  above  described.  A  layer  of  intramembranous 
bone  thus  surrounds  the  endochondral  bone  in  bones  preformed  in 
hyaline  cartilage.  The  two  modes  of  ossification  may,  therefore, 
be  observed  in  either  a  cross  or  a  longitudinal  section  of  a  develop- 
ing bone  preformed  in  hyaline  cartilage.  In  such  preparations 
the  endochondral  bone  can  be  readily  distinguished  from  the  intra- 


I 

.©     •• 


Osteo v 

blast. 


_  ^J^ -Primary 

$\     *        .--  .-•;'-        marrow 

^       &J&  Space" 

&        «x' 


Osseous 

•""'•-' g5\_   ~®~~    tissue. 

f*  &?$£{??* 
•    ( 


Fig.  85. — Section  through  the  lower  jaw  of  an  embryo  sheep  (decalcified  with  picric 
acid)  ;  y(  300.  At  a  and  immediately  below  are  seen  the  fibers  of  a  primitive  marrow 
cavity  lying  close  together  and  engaged  in  the  formation  of  the  ground-substance  of  the 
bone,  while  the  cells  of  the  marrow  cavity,  with  their  processes,  arrange  themselves  on 
either  side  of  the  newly  formed  lamella  and  functionate  as  osteoblasts. 


membranous  bone  by  reason  of  the  fact  that  remnants  of  calcified 
cartilage  matrix  may  be  observed  in  the  osseous  trabeculae  of  the 
former.  It  will  be  remembered  that  these  osseous  trabeculae  de- 
velop about  the  calcified  cartilage  matrix  remaining  after  the  dis- 
appearance of  the  cartilage -cells.  In  figure  86,  which  shows  a 
cross-section  of  a  bone  from  the  leg  of  a  human  embryo,  these  facts 
are  clearly  shown.  A  study  of  this  figure  shows  the  endochondral 
bone,  with  the  remnants  of  the  cartilage  matrix  (shaded  more 


THE    CONNECTIVE    TISSUES.  115 

deeply)  inclosed  in  osseous  tissue,  making  up  the  greater  portion 
of  the  section  and  surrounded  by  the  intramembranous  bone. 

In  figure  87,  more  highly  magnified,  the  relations  of  endochon- 
dral to  intramembranous  bone  and  the  details  of  their  mode  of 
development  are  shown  ;  also  the  structure  of  the  periosteum. 

As  was  stated  in  the  previous  section,  soon  after  the  formation 
of  the  endochondral  bone,  this  is  again  absorbed  ;  the  process  of 
endochondral  bone-formation  and  absorption  extending  from  the 
center  of  ossification  toward  the  ends  of  the  diaphysis.  Before  the 
absorption  of  the  endochondral  bone,  the  intramembranous  bone 
has  attained  an  appreciable  thickness  and  surrounds  the  marrow 
cavity  formed  on  the  absorption  of  the  endochondral  bone.  Before, 


Fig.  86. — Cross- section  of  developing  bone  from  leg  of  human  embryo,  showing  endo- 
chondral and  intramembranous  bone-development. 

however,  the  marrow  cavity  can  attain  its  full  dimensions,  much  of 
the  intramembranous  bone  must  also  undergo  absorption.  While 
intramembranous  bone  is  being  developed  from  the  periosteum  and 
thus  added  to  the  outer  surface  of  that  already  formed,  osteoclasts 
are  constantly  engaged  in  its  removal  from  the  inner  surface  of  the 
intramembranous  bone.  The  marrow  cavity  is  thus  enlarged,  the 
process  continuing  until  the  shaft  attains  its  full  size. 

The  compact  bone  of  the  shaft  is  developed  from  the  primary 
spongy  intramembranous  bone  after  the  following  manner  :  The 
primary  marrow  spaces  are  enlarged  by  an  absorption,  through  the 
agency  of  osteoclasts,  of  many  of  the  smaller  trabeculae  of  osse- 


n6 


THE     TISSUES. 


ous  tissue  and  by  a  partial  absorption  of  the  larger  ones,  the 
primary  marrow  spaces  thus  becoming  secondary  marrow  spaces,  or 
Haversian  spaces.  The  osteoblasts  now  arrange  themselves  in  layers 


Connective- 
tissue. 


Outer  fibrous  - 
layer  of 
pe'riosteum. 


. 


Osteogenetic- 
layer  of 
periosteum. 


Osteoblasts 


Marrow- 
space. 

Blood-ves- 
sel. 

Osteoblasts.  - 


Remnants  of 
cartilage 
matrix. 

Bone-cells.-, 


Osseous 

matrix.'   '  '^.<'0 

s& 

Osteoblasts.,-'" 


Fig.  87. — From  a  cross-section  of  a  shaft  (tibia  of  a  sheep)  ;  X  55°-  I*1  t^e  lower 
part  of  the  figure  is  endochondral  bone-formation  (the  black  cords  are  the  remains  of  the 
cartilaginous  matrix)  ;  in  the  upper  portion  is  bone  developed  from  the  periosteum. 


about  the  walls  of  the  Haversian  spaces  and  deposit  lamella  after 
lamella  of  bone  matrix,  concentrically  arranged,  until  the  large 
Haversian  spaces  have  been  reduced  to  Haversian  canals.  During 


THE    CONNECTIVE    TISSUES.  I  I/ 

this  process  many  of  the  osteoblasts  become  inclosed  in  bone 
matrix,  forming  bone-cells  and  the  blood-vessels  of  the  Haversian 
spaces  remain  as  the  vessels  found  in  the  Haversian  canals.  The 
spongy  intramembranous  bone  not  absorbed  at  the  commencement 
of  the  formation  of  the  system  of  concentric  lamellae,  remains 
between  the  concentric  systems  as  interstitial  lamellae.  The  circum- 
ferential lamellae  are  those  last  formed  by  the  periosteum.  Calcifica- 
ation  of  the  osseous  matrix  takes  place  after  its  formation  by  the 
osteoblasts. 

From  what  has  been  stated  it  may  be  seen  that  the  shafts  of 
the  long  bones  and  bones  not  preformed  in  cartilage  develop  by  the 
process  of  intramembranous  bone-formation,  while  the  cancellous 
bone  in  the  ends  of  the  diaphysis  and  in  the  epiphyses  is  endochon- 
dral  bone.  Further,  that  long  bones  grow  in  length  by  endo- 
chondral  bone-development,  and  in  thickness  by  the  formation  of 
intramembranous  bone.  In  the  development  of  the  smaller  irreg- 
ular bones,  both  processes  may  be  engaged  ;  the  resulting  bone  can 
not,  however,  be  so  clearly  defined. 


TECHNIC 

133.  One  of  the  methods  for  examining  connective-tissue  cells  and 
fibers  is  that  recommended  by  Ranvier  (89)  ;  it  is  as  follows  :   The  skin 
of  a  recently  killed  dog  or  rabbit  is  carefully  raised,  and  a  0.1%  aqueous 
solution  of  nitrate  of  silver  injected  subcutaneously  by  means  of  a  glass 
syringe.     The  result  is  an  edematous  swelling  in  which  the  connective- 
tissue  cells  and  fibers  (the  latter  somewhat  stretched)  come  into  imme- 
diate contact  with  the  fixing  fluid  and  are  consequently  preserved  in  their 
original  condition.      In  about  three-quarters  of  an  hour  the  whole  eleva- 
tion should  be  cut  out  (it  will  not  now  collapse)  and  small  fragments 
placed  upon  a  slide  and  carefully  teased.      Isolated  connective-tissue  cells 
with  processes  of  different  shapes,  having  the  most  varied  relations  to 
those  from  adjacent  cells,  are  seen.     The  fibers  themselves  either  consist 
of  several  fibrils,  or,  if  thicker,  are  often  surrounded  by  a  spirally  encir- 
cling fibril.      By  this  method  numerous  elastic  fibers  and  fat-cells  are  also 
brought  out.     If  a  drop  of  picrocarmin  be  added  to  such  a  teased  prepa- 
ration and  the  whole  allowed  to  remain   for  twelve    hours  in  a  moist 
chamber,  and  formic  glycerin  (a  solution  of   i   part  formic  acid  in    100 
parts  glycerin)  be  then  substituted  for  twenty-four  hours,  the  following  in- 
structive picture  is  obtained  :   All  nuclei  are  colored  red,  the  white  fibrous 
connective-tissue  fibers  pink,  the  fibrils  encircling  the  latter  brownish- 
red,   and  the  elastic  fibers  canary  yellow.     The  peripheral  protoplasm 
of  the  fat -cells  is  particularly  well  preserved,  a  condition  hardly  obtain- 
able by  any  other  method. 

134.  Connective  tissue  with  a  parallel  arrangement  of  its  fibers  is  best 
studied  in  tendon,  those  in  the  tails  of  rats  and  mice  being  particularly 
well  adapted  to  this  purpose.      If  one  of  the  distal  vertebrae  of  the  tail  be 
loosened  and  pulled  away  from  its  neighbor,  the  attached  tendons  will 
become  separated  from  the  muscles  at  the  root  of  the  tail  and  appear  as 
thin  glistening  threads.     These  are  easily  teased  on  a  slide  into  fibers  and 


IlS  THE     TISSUES. 

fibrils.  Such  preparations  are  also  useful  in  studying  the  action  of  reagents 
(see  below). 

The  substance  resembling  mucin  which  cements  the  fibrillae  together 
is  soluble  in  lime-water  and  baryta-water — a  circumstance  made  use  of 
and  recommended  by  Rollet  (72,  II)  as  a  method  for  the  isolation  of 
connective -tissue  fibrils.  In  necrotic  tissue  the  fibers  show  a  degenera- 
tion into  fibrils  (Ranvier,  89). 

If  connective  tissue  be  heated  in  water  or  dilute  acids  to  120°  C.,  and 
the  fluid  then  filtered,  a  solution  is  obtained  from  which  collagen  can  be 
precipitated  by  means  of  alcohol.  This  is  insoluble  in  cold  water,  alcohol, 
and  ether,  but  is  soluble  in  hot  water  and  when  dissolved  in  the  latter  and 
cooled,  becomes  transformed  into  a  gelatinous  substance.  Unlike  mucin 
and  chondrin  this  substance  does  not  precipitate  on  the  addition  of  acetic 
and  mineral  acids.  Tannic  acid  and  corrosive  sublimate  will  cause  pre- 
cipitation, as  also  in  the  case  of  chondrin,  but  not  with  mucin  (vid.  also 
Hoppe-Seyler). 

135.  Elastic  tissue  may  be  obtained  by  treating  connective   tissue 
with  potassium  hydrate  solution,  and  if  the  alveoli  of  the  lungs  be  treated 
for  some  time  with  this  reagent,  very  small  elastic  fibers  can  be  obtained. 
By  this  means  the  connective-tissue  fibers  are  dissolved,  but  not  the  elastic 
fibers.      Particularly  coarse  fibers  are  found  in  the  ligamenta  subflava. 

136.  According  to  Kiihne,  connective  and  elastic  tissues  are  differ- 
ently affected  by  trypsin   digestion — /.  e.,  alkaline  glycerin -pancreas 
extract  at  35°  C. — white  fibrous  connective  tissue  being  resolved   into 
fibrils,  while  elastic  tissue  is  entirely  dissolved. 

137.  Elastic  fibers  remain  unchanged  in  acetic  acid,  and  even  when 
boiled  in  a  20%   solution  they  only  become  slightly  brittle.     They  are, 
however,  rapidly  destroyed  by  concentrated  hydrochloric  acid,  although 
in  a  10%  solution  at  ordinary  temperature  no  change  is  seen.     In  a  50% 
solution  the  fiber  is  dissolved  in  seven  days,  and  in  a  concentrated  solu- 
tion in  two  days.     The  inner  substance  of  the  fiber  is  first  attacked,  then 
the  membrane.     To  demonstrate  this  membrane,  the   fibers  are  -boiled 
several  times  in  concentrated  hydrochloric  acid  and    the   whole    then 
poured  into  cold  water.      Occasionally,  a  longitudinal  striation  of  the 
membrane  is  seen,  indicating  a  fibrillar  structure.     Concentrated  solutions 
of  potassium  hydrate  disintegrate  the  fibers  in  a  few  days  ;  weak  solutions, 
more  slowly.      A   i  %   solution  of  potassium  hydrate  requires  months  to 
produce  the  effect;  a   2%    solution,   one  month;  a  5%,  three  days;  a 
10%,  one  day  ;  and  20%  to  40%,  only  a  few  hours.     A  weak  solution 
of  potassium  hydrate,  even  when  brought  to  the  boiling-point,  does  not 
dissolve  elastic  fibers,  nor  does  it  cause  them  to  become  brittle.      If,  how- 
ever, they  be  boiled  in  a  5%  or  10%  solution  of  potassium  hydrate,  the 
membranes  of  the  fibers  will  be  isolated.      A  cold  20%  solution  has  the 
same  effect  in  one  or  two  days.      Pepsin  induces  a  disintegration  of  the 
contents  of  the  fiber,  leaving  the  membranes  intact  (F.  P.  Mall). 

138.  Orcein,  if  correctly  applied,  colors  elastic  fibers  a  dark  brown, 
and  can  be  used  to  demonstrate  them  in  sections  (Unna,   91).     The 
solution  is  made  as  follows:    T^-  gm.  of  orcein  is  dissolved  in  20  c.c. 
95%  alcohol  and  5  c.c.  distilled  water.     This  is  then  diluted  one-half 
by  adding  a  solution  composed  of  o.i  c.c.   hydrochloric  acid,  20  c.c. 
95%   alcohol,   and    5    c.c.    distilled  water.     The    sections   are    stained 
for  twenty-four  hours  and   differentiated    in  acid  alcohol    for   about   a 


THE    CONNECTIVE    TISSUES.  I  19 

minute.  Then  the  nuclei  may  be  stained  either  witn  hematoxylin  or 
methylene-blue,  and  the  specimens  carried  over  into  absolute  alcohol, 
next  into  xylol,  and  finally  mounted  in  Canada  balsam. 

139.  Trypsin  quickly  dissolves  elastic  fibers,   but  not  tendon  and 
reticulated  tissue,  the  latter  remaining  unchanged  for  days.      Putrefaction 
disintegrates  the  ligamentum  nuchae  in  a  few  days,  the  internal  structure 
of  the  fibers  suffering  first,  the  membranes  last. 

140.  To  demonstrate  the  inner  substance  of  elastic  fibers  and  their 
membranes,   magenta  red  has  been  recommended  (a  small  granule  is 
added   to   50   c.c.    glycerin  and  50  c.c.   water).      By  this  method  the 
internal  substance  is  colored  red  while  the  enveloping  sheath  remains 
colorless. 

141.  To  F.  P.  Mall  also  belongs  the  credit  for  a  few  data,  which  we 
insert,  as  to  the  different  reactions  which  various  connective-tissue  sub- 
stances show  when  treated  by  the  same  reagents. 

When  a  tendon  is  boiled  it  becomes  shorter,  but  if  it  be  fixed  before 
boiling,  there  is  no  change.  Adenoid  reticulum  shrinks  when  boiled,  but 
after  a  short  time  swells,  and  finally  dissolves.  Both  tendon  and  adenoid 
reticulum  shrink  at  70°  C.  If,  however,  they  be  first  treated  with  a 
0.5$  solution  of  osmic  acid,  the  shrinkage  will  not  take  place  until 
95°  C.  is  reached.  If  the  reticulum  or  the  tendon  has  become  shrunken 
through  heat,  they  are  easily  digested  with  pancreatin,  and  putrefy  very 
readily.  Tendon  fibers  do  not  become  swollen  in  glacial  acetic  acid, 
either  concentrated  or  in  strengths  of  0.05%  or  less,  but  in  strengths 
of  0.5^  to  25%  they  swell,  and  if  placed  in  a  25%  solution  they  will 
dissolve  in  twenty-four  hours.  They  also  swell  in  hydrochloric  acid  in 
strengths  of  0.1%  to  6%.  In  strengths  of  6C/C  to  25%  the  fibers  remain 
unchanged  for  some  time,  and  only  dissolve  in  a  concentrated  solution 
of  this  acid.  Reticulated  tissue,  on  the  other  hand,  swells  in  a  3% 
hydrochloric  acid  solution,  but  remains  unchanged  in  strengths  of  3  %  to 
10%.  It  dissolves  in  twenty-four  hours  in  solutions  of  25%  and  over. 
After  treatment  with  a  dilute  solution  of  acid,  tendon  dissolves  more  rapidly 
on  boiling  than  does  reticular  tissue. 

Tendon  exposed  to  the  action  of  the  gastric  juice  of  a  dog  does  not 
dissolve  more  rapidly  than  elastic  tissue  ;  but  if  placed  in  an  artificial  solu- 
tion of  gastric  juice,  tendon  dissolves  first,  then  reticular  tissue,  and  finally 
elastic  fibers.  Pancreatin  affects  neither  tendon  nor  reticulated  tissue,  but 
if  boiled,  both  tissues  are  easily  digested  by  its  action.  If  taken  out  of 
the  body,  neither  tendon  nor  reticulum  will  become  affected  by  putre- 
faction. In  the  body,  however,  and  especially  at  high  temperatures 
(37°  C-)»  both  tissues  are  decomposed  within  a  few  days. 

142.  Fresh  adipose  tissues  can  be  obtained  in  lobules  and  in  small 
groups  of  cells  from  the  mesenteries  of  small  animals.     As  a  rule,  the 
highly  refractive  fat  globule  hides  from  view  the  nucleus  and  protoplasm 
of  the  cell.     The  latter  structures  can  be  brought  out  by  the  subcutaneous 
injection  of  silver  nitrate  solution,  this  forming  the  edematous  elevation 
previously  described  (vid.  T.   133).      Fresh  fat  is  soluble  in  ether  and 
chloroform,  especially  if  the  latter  be  heated.      Strong  sulphuric  acid  does 
not  dissolve  fat.     The  stains  made  from  the  root  of  the  henna  plant  color 
fat  red  (the  color  disappearing  in  ethereal  oils).    Quinolin-blue,  dissolved 
in  dilute  alcohol,  stains  fat  a  dark  blue.      If  a  40%   potassium  hydrate 
solution    be    then    added,    everything   will    become    decolorized    except 


1 2O  THE     TISSUES. 

the  fat.  The  most  important  reagent  for  demonstrating  adipose  tissue  is 
osmic  acid  (and  its  mixtures).  Small  pieces  of  adipose  tissue  are 
treated  for  twenty -four  hours  with  a  0.5  c/c  to  i  %  osmic  acid  solution  ;  if 
mixtures  containing  osmic  acid  be  used,  the  specimens  are  generally  im- 
mersed for  a  somewhat  longer  period.  The  pieces  are  then  washed  with 
water,  and  should  not  be  placed  directly  into  alcohol  of  full  strength,  as 
all  the  structures  would  then  become  intensely  black  (Flemming,  89),  but 
carried  into  alcohols  of  ascending  strength.  When  treated  in  this  way  the 
globules  of  fat  take  a  more  intense  stain  than  the  other  tissues,  which, 
nevertheless,  are  blackened  to  some  extent. 

143.  Fat  that  has  been  subjected  to  osmic  acid  treatment  dissolves 
readily  in  turpentine,  xylol,  toluol,  ether,  and  creosote,  with  difficulty  in 
oil  of  cloves,  and  not  at  all  in  chloroform.      Such  preparations  are  best 
carried  from  chloroform  into  paraffin.      Fat  that  has  been  stained  with 
osmic  acid  can  be  decolorized  by  nascent  chlorin.     The  specimens  are 
placed  in  a  jar  of  alcohol  in  which  crystals  of  potassium  chlorid  have 
been  previously  placed.      Hydrochloric  acid  is  then  added  (to  i%)  and 
the  vessel  tightly  sealed  (P.  Mayer,  81). 

144.  L.  Daddi  has  recently  recommended  Sudan  III  as  a  stain  for  fat. 
This  reagent  can  be  applied  in  two  ways  :    ( i )  Either  the  animals  are  fed 
with  the  coloring  matter  for  some  days,  in  which  case  all  the  fat  will  be 
colored  red,  or  (2)  either  fresh  or  fixed  pieces  of  tissue  or  sections  are 
stained.      Fixation  before  staining  must  be  done  in  media  that  do  not  dis- 
solve fat,  as,  for  instance,  Miiller's  fluid.     A  saturated  alcoholic  solution 
of  the  stain  is  used  and  allowed  to  act  from  five  to  ten  minutes.     The 
specimen  is  then  washed  with  alcohol  and  mounted  in  glycerin.     The 
author's  experiments  with  Sudan  have  been  very  satisfactory. 

145.  Thin  lamellae  of  fresh  cartilage  are  examined  after  separating 
them  from  the  soft  parts  and  placing  them  in  indifferent  fluids.      Cartilage 
removed  from  the  hyposternum  or  episternum  or  scapula  of  a  frog  is 
especially  adapted  for  examination.      Larger  pieces  of  uncalcified  carti- 
lage may  be  used  if  cut  into  sufficiently  thin  sections  with  a  razor  moist- 
ened with  an  indifferent  fluid.    Under  the  microscope  such  sections  show 
a  finely  punctated  background  with  capsules  containing  cartilage-cells, 
provided  the  latter  have  not  fallen  out  in  the  process  of  cutting,  in  which 
case  lacunae  will  be  observed. 

146.  Osmic  acid  and  corrosive  sublimate  are  by  far  the  best  fix- 
ing agents  for  cartilage.      If  the  cartilage  be  calcified,  it  is  fixed  for  some 
time  in  picric  acid,  which  at  the  same  time  acts  as  a  decalcifying  agent. 
Although  alcohol  fixes  cartilage  fairly  well,   it  causes  shrinkage  of  the 
cells.     The   ground  substance    may  be   specifically    colored  by   certain 
reagents,  safranin  producing  an  orange  and  hematoxylin  a  blue  stain. 

147.  On    treating    cartilage    by  certain    methods,  systems    of  lines 
appear  in  its  ground  substance,  possibly  indicating  a  canalicular  sys- 
tem in  the  cartilage.      In  order  to  make  these  structures  visible,  Wolters 
recommends  staining  thin  sections  for  twenty-four  hours  in  a  dilute  solu- 
tion of  Delafield's  hematoxylin  (violet  blue)  (ind.  T.  62).     They  are  then 
treated  with  a  concentrated  alcoholic  solution  of  picric  acid. 

148.  The  capsules  are  seen  to  best  advantage  if  small  pieces  of  car- 
tilage are  treated  with  a  i%  solution  of  gold  chlorid. 

149.  Connective-tissue    and    elastic    fibers    in    cartilage   are    easily 


THE    CONNECTIVE    TISSUES.  121 

demonstrated  by  staining  the  specimens  with  picrocarmin.  The  con- 
nective-tissue fibers  are  colored  a  pale  pink,  the  elastic  fibers  yellow. 
The  latter  may  also  be  stained  with  a  i  f/0  aqueous  solution  of  acid 
fuchsin. 

150.  If  a  section  of  fresh  cartilage  be  placed  in  a  weak  solution  of 
iodo=iodid  of  potassium   (Lugol's  solution),  glycogen  can  sometimes 
be  seen  in  the  cartilage-cells,  stained  a  peculiar  mahogany  brown.      If 
elastic  fibers  be  present,  they  also  are  stained  brown,  but  of  a  different 
shade. 

151.  Thin  bone  lamellae,  such  as  occur  in  the  walls  of  the  ethmoidal 
cells,  can  be  cleaned  of  all  the  soft  parts  and  examined  without  further 
manipulation.      If  larger  bones  are  scraped  with  a  sharp  knife,   pieces 
suitable  for  microscopic  examination  are  sometimes  obtained. 

152.  If,  however,  the  denser  structure  of  the  large  bones  is  to  be  more 
closely  examined,  the  following  is  the  best  procedure :     A  long  bone  is 
thoroughly  freed  from  fat  and  other  soft  parts  by  allowing  it  to  macerate, 
after  which  it  is  thoroughly  washed  and  dried,  thus  freeing  it  from  its 
organic  material.     Then,  by  means  of  two  parallel  cuts  with  a  saw,  as 
thin  a  disc  as  possible  is  cut  out.     The  section  is  now  ground  still  thin- 
ner, either  between  two  hones  or  upon  a  piece  of  glass  covered  with 
emery.      One  surface  of  the  bone  is  then  polished  and  fastened  by  means 
of  heated    Canada   balsam    to   a   thick   square    plate  of  glass   with  the 
polished  side  toward  the  glass.      Care  should  be  taken  that  no  air-bubbles 
are  inclosed  between  the  section  and  the  glass.     As  soon  as  the  specimen 
is  firmly  adherent,  the  other  side  is  ground  upon  the  emery  plate  or  hone, 
during  which  manipulation  the  glass  to  which  the  bone  has  been  fastened 
is  held  between  the  fingers.     As  soon  as  the  section  is  sufficiently  thin 
and  transparent,  it  is  polished.      In  order  to  remove  the  Canada  balsam 
and  powdered  bone  from  the  section,  the  glass  and  bone  are  dried  and 
placed  in  some  solvent  of  Canada  balsam,  such  as  xylol.     This  loosens  the 
specimen  from  the  glass,  after  which  it  is  immersed  in  absolute  alcohol, 
thoroughly   washed,  and    dried    in    the   air.      On  examining    the    bone 
through  the  microscope,  its  lacunas  will  appear  black  on  a  colorless  back- 
ground.    The  reason  is,  that  the  air  has  taken  the  place  of  the  evapo- 
rated alcohol  and  the  spaces  appear  black  by  direct  light. 

153.  Sections  thus  prepared  may  be  permanently  mounted  as  follows  : 
Small   pieces  of  dry  Canada  balsam  are  placed  both  upon  a  slide  and  a 
cover-glass  and  warmed  until  they  have  become  fluid,  then  allowed  to 
cool    until    a    thin   film  forms  over  the  balsam ;  the  bone  disc  is  then 
placed    upon  the  balsam  on   the    slide   and  quickly   covered   with    the 
cover-glass.      A  firm  pressure  will   evenly  distribute  the  balsam,  and  if 
the  whole  has  been  done  with  sufficient  rapidity  the  air  will  have  been 
caught  in  the  open  spaces  of  the  bone  before  the  Canada  balsam  has  had 
a  chance  to  enter  these  spaces. 

154.  Other  substances  may  be  used  to  demonstrate  the  spaces  in 
bone.      Ranvier  (75)  recommends  the  following  method:     A  few  c.c. 
of  a  concentrated  alcoholic  solution  of  anilin  blue  (which  is  soluble  in 
alcohol  and  not  soluble  in  water  and  sodium  chlorid  solution)  are  placed 
in  an  evaporating  dish  containing  the  dry  bone.     The  solution  is  very 
carefully  evaporated,  as  the  alcohol  may  otherwise  ignite.     The  specimen, 
which  will  soon  be  covered  on  both  surfaces  by  a  blue  powder,  is  taken  out 
and  ground  upon  a  rough  glass  plate  until  thoroughly  clean.     While  being 


122  THE    TISSUES. 

polished  the  bone  should  be  kept  moist  by  a  solution  of  sodium  chlorid 
(vid.  T.  13).  On  heating  in  the  evaporating  dish,  the  air  is  driven  from 
the  spaces  and  replaced  by  the  anilin  blue.  As  already  stated,  anilin 
blue  is  insoluble  in  sodium  chlorid  solution,  and  it  therefore  remains  un- 
affected by  the  latter  during  the  process  of  grinding  and  cleaning. 
Hence  it  remains  in  the  lacunae  and  canaliculi  of  the  bone,  which  then 
appear  blue.  The  specimen  may  either  be  mounted  in  glycerin -sodium 
chlorid  and  the  edge  of  the  cover-glass  sealed  with  varnish  (vid.  T.  99), 
or  the  section  may  be  washed  for  a  short  time  in  water  (in  order  to 
remove  the  sodium  chlorid),  dried,  and  finally  mounted  in  Canada 
balsam  as  directed. 

155.  In  bone,  as  also  in  cartilage,  there  sometimes  occur  amorphous 
as  well  as  crystalline  deposits  of  lime-salts.      Upon  the  addition  of  acetic 
acid  the  carbonate  of  calcium  gives  off  bubbles  ;  upon  the  addition  of 
sulphuric  acid,  short,  thin  needles  will  be  formed — crystals  of  gypsum. 
Hematoxylin  stains  the  lime-salts  blue,  with  the  exception  of  the  oxalate 
of  lime.     Alkaline  solution    of  purpurin  stains  calcium  carbonate  red. 
Caustic  potash  does  not  affect  lime. 

156.  In  order  to   study  the  organic  constituents  of  bone,   it  must 
first  be  decalcified  and  thus  rendered  suitable  for  sectioning — /.  e. ,  the 
lime-salts  must  first  be  removed,  and  that  without  destroying  the  cellular 
elements  of  the  bone.     The  process  of  decalcification  consists  in  substi- 
tuting the  acids  of  the  decalcifying  fluids  for  those  of  the  bone  salts. 
As  a  consequence,  new  combinations  are  formed,  soluble  in  water  or  in 
an  excess  of  the  decalcifying  acids  themselves. 

157.  The  decalcifying  fluids  most  frequently  used  are  : 

(a)  Hydrochloric  acid  (i%  aqueous  solution),  used  in  quantities 
amounting  to  about  fifty  times  the  volume  of  the  specimen.  The  solution 
is  changed  daily,  and  the  bone  remains  immersed  until  it  is  soft  enough 
to  be  cut.  This  stage  is  reached  when  a  needle  can  be  introduced  with 
no  resistance. 

(b}  An  aqueous  solution  of  nitric  acid  m  strengths  of  3%  to  10%,  ac- 
cording to  the  delicacy  of  the  specimen,  and  of  a  specific  gravity  of  1.4. 
Instead  of  water,  70%  alcohol  may  be  used  as  a  solvent  for  the  acid. 
Thoma  has  recommended  for  this  purpose  a  solution  consisting  of  i 
vol.  nitric  acid  of  a  specific  gravity  of  1.3,  and  5  vols.  alcohol.  This 
fluid  is  changed  daily  and  decalcifies  small  objects  in  a  few  days.  The 
specimens  are  then  washed  several  times  in  70%  alcohol  to  remove 
as  much  as  possible  of  the  acid.  95%  alcohol,  with  the  addition 
of  a  little  precipitated  calcium  carbonate,  has  been  recommended  for 
washing  sections  that  have  been  treated  by  Thoma' s  method.  After  from 
eight  to  fourteen  days  the  specimens  are  again  washed  with  clear  95% 
alcohol. 

(c)  The  process  of  decalcification  recommended  by  v.  Ebner  (75)  is 
of  considerable  value,  as  it  also  reveals  the  fibrillar  structure  of  the 
bone  lamellae.  A  cold  saturated  solution  of  sodium  chlorid  is  diluted 
with  2  vols.  of  water,  and  2  %  of  hydrochloric  acid  added.  This  fluid 
decalcifies  very  slowly,  and  must  either  be  changed  daily  or  a  small 
quantity  of  hydrochloric  acid  occasionally  added.  As  soon  as  the  speci- 
men is  thoroughly  decalcified,  it  is  washed  with  a  half-saturated  solution 
of  sodium  chlorid.  A  little  ammonia  is  now  added  from  time  to  time 
until  the  reaction  of  the  fluid  and  bone  is  neutral. 


MUSCULAR     TISSUE.  123 

Very  small  pieces  that  contain  very  little  lime-salts,  as,  for  in- 
stance, bones  in  an  embryonal  condition  where  calcification  has  only  just 
begun,  can  be  deprived  of  their  lime-salts  by  means  of  acid  fixing  solu- 
tions like  Flemming's  fluid,  chromic  acid,  picric  acid,  etc. 

(e)  Bone  should  be  first  fixed  in  some  one  of  the  fixing  fluids  and 
then  decalcified. 

158.  A  method  adapted   to   the  study  of  the  hard   and  soft  parts 
together  is  that  first  used  by  von  Koch  in  studying  corals.     The  specimen 
is  first  fixed,  and  if  it  be  a  long  bone,  the  marrow  cavity  should  first  be 
opened  to  permit  the  fixing  agent  to  come  in  contact  with  all  parts  of  the 
tissue.     After   fixing,  the   bone  is  stained  and  then  placed  in  absolute 
alcohol,  and  when  completely  dehydrated  the  pieces  are  placed  in  chloro- 
form, then  in  a  thin  solution  of  Canada  balsam  in  chloroform,  and  finally 
put  into  an  oven  kept  at  a  temperature  of  about  50°  C.  for  from  three  to 
four  months.      By  this  means  the  pieces  are  completely  penetrated  by 
the  Canada  balsam,  and  as  the  latter  becomes  very  hard  on  cooling,  the 
sections  may  be  afterward  ground  without  difficulty.      Long  as  this  pro- 
cedure  may  seem,  it   is  still   the  one   which  enables  us  to  see    the  soft 
and  hard  parts  of  bone  in  a  relationship  the  least  changed  by  manipu- 
lation. 

159.  Sections  treated  by  Ranvier's   method  (vid.  T.   154)  show  the 
perforating  fibers  of  Sharpey  as  bright,  sharply  defined  ribbons,  appearing 
as  streaks  or  circles,  according  to  the  section  made  (longitudinal  or  trans- 
verse).    If  decalcified  specimens  be  first  rendered  transparent  by  glacial 
acetic  acid,  and  then  immersed  for  a  minute  in  a  concentrated  aqueous 
solution  of  indigocarmin,  washed  with  water,  and  then  mounted  in  gly- 
cerin or  Canada  balsam,  the  fibers  of  Sharpey  will  appear  red  and  the 
remaining  structures  blue.      Thin  sections  of  bone  can  be  deprived  of 
their  organic  elements  by  bringing  them  for  from  one-half  a  minute  to  a 
minute  into  a  platinum  crucible  at  a  red  heat.      In  such  preparations  cal- 
cified Sharpey 's  fibers  may  be  seen  (Kolliker,  86). 

1 60.  Virchow's  bone  corpuscles  may  be  isolated  in    the   following 
manner :   Very  thin  fragments  or  discs  of  bone  are  immersed  for  some 
hours  in  concentrated  nitric  acid.     They  are  then  placed  on  a  slide  and 
covered  with  a  cover-glass ;  pressure  with  a  needle  upon  the  latter  will 
isolate  the  lacunae,  and  occasionally  also  their  numerous  processes,  the 
canal  iculi. 


C  MUSCULAR  TISSUE. 

Almost  all  the  muscles  of  vertebrates  have  their  origin  from  the 
middle  germinal  layer.  In  the  simplest  type  the  protoplasm  of  the 
formative  cell  changes  into  contractile  muscle  substance,  the  cell  in 
the  meantime  undergoing  a  change  in  shape  (unstriped  muscle-cell). 
In  other  cases  contractile  fibrils  are  formed  which  are  separated  by 
the  remains  of  the  undifferentiated  protoplasm  (striped  muscle-cells). 
In  this  case  the  cells  either  increase  very  little  in  length  and  possess 
only  a  single  nucleus  (heart  muscle),  or  they  grow  considerably 
longer  and  develop  many  nuclei  (voluntary  skeletal  and  skin 
muscles). 


124 


THE     TISSUES. 


A  peculiarity  of  muscle-substance  is  that  it  contracts  in  only 
one  direction,  while  undifferentiated  protoplasm  contracts  in  all 
directions. 

I.  NONSTRIATED  MUSCLE-CELLS. 

The  smooth,  unstriped,  nonstriated  or  vegetative  muscle-cells 
belong  to  involuntary  muscle,  and  are 
found  in  the  walls  of  the  intestine, 
trachea,  and  bronchi,  genito-urinary  ap- 
paratus, blood-vessels,  in  certain  glands, 
and  also  in  connection  with  the  hair  fol- 
licles of  the  skin.  The  involuntary  mus- 
cle-cells are  spindle-shaped  cells,  whose 
substance  either  appears  homogeneous 
or  shows  a  faint,  longitudinal  striation. 
They  are  40-200  //  long  and  3-8  p.  broad. 
The  longest  are  found  in  the  pregnant 
uterus,  where  they  attain  a  length  of 
500  p.  At  the  thickened  middle  portion 
of  the  cell  is  a  long  rod-like  nucleus, 
typic  of  this  class  of  cells.  Surrounding 
it,  and  especially  at  its  ends,  is  a  small 
quantity  of  undifferentiated  protoplasm. 
Nonstriated  muscle-cells  are  doubly  re- 
fractive— anisotropic.  Nonstriated  mus- 
cle-cells are  cemented  together,  by  a 
small  amount  of  intercellular  cement,  to 
form  membranes  or  small  bundles  (fas- 
ciculi) surrounded  by  a  thin  layer  of 
fibrous  connective  tissue.  They  are  often 
joined  by  longitudinal  ridges  similar  to 
the  prickles  of  epidermal  cells.  These 
fit  edge  to  edge  and  form  connecting 
bridges  (Kultschitzky,  Barfurth). 


Nucleus. 
-  Protoplasm. 


Fig.  88. — Smooth  muscle- 
cells  from  the  intestine  of  a  cat : 
In  I,  isolated ;  in  2  and  3,  in 
cross-section  ;  X  3°°-  Technic 
No.  172.  At  a  the  cell  is  cut 
in  the  plane  of  the  nucleus  ;  at 
c,  in  the  neighborhood  of  the 
pointed  end.  In  3  (from  Bar- 
furth) is  seen  the  manner  in 
which  neighboring  cells  are 
joined  to  each  other  by  inter- 
cellular bridges. 


2.  STRIPED  MUSCLE-FIBERS. 
Soon  after  the  segmentation  of  the 
mesoderm  begins,    certain   cells    of  the 

mesoblastic  somites  commence  the  formation  of  muscle  -  sub- 
stance in  their  interior,  a  process  which  is  accompanied  by  in- 
crease in  the  number  of  nuclei,  the  formation  of  a  membrane,  a 
lengthening  of  the  cells,  and  the  appearance  of  fibrils  in  the  per- 
ipheral protoplasm  of  the  cells. 

Voluntary  or  striated  muscle-cells  are  large,  highly  differen- 
tiated, polynuclear  cells,  which  may  attain  a  length  of  12  cm.,  with 
a  width  of  10— IOO  //.  They  are  consequently  known  as  muscle-fibers. 
Their  free  ends  are  usually  pointed ;  the  ends  attached  to  tendon 
rounded  (Fig.  90). 


MUSCULAR     TISSUE. 


125 


Each  striated  muscle-fiber  consists  of  a  delicate  membrane,  the 
sarcolcmma,  a  muscle  protoplasm,  in  which  are  recognized  very  fine 


- —  Free  ending. 


~-»  Nucleus. 


>  Muscle- 
substance. 

Sarcolemma. 


Fig.  89. — Cross- section  of  striated  muscle-fibers  : 
I,  Of  man  ;  2,  of  the  frog.  The  relations  of  the 
nuclei  to  the  muscle-substance  and  sarcolemma  are 
clearly  visible  ;  X  670. 


Fig.  90. — Muscle-fiber  from 
one  of  the  ocular  muscles  of  a 
rabbit,  showing  its  free  end ; 

Xi75- 


fibrils  and  a  semifluid  interfibrillar  substance  (the  sarcoplasm)  and 
the  muscle  nuclei.  The  sarcolemma  is  a  very  delicate,  transparent, 
and  apparently  structureless  membrane,  which  resists  strong  acetic 
acid,  even  after  boiling  for  a  long  time.  If  we  examine  in  an  indif- 
ferent fluid  fresh  muscle-fibers,  the  contents  of  which  have  been 


Fig.  91. — Striated  muscle-fiber  of  frog,  showing 
sarcolemma. 


Fig.  92. — Diagram  of  the 
structure  of  the  fibrils  of  a  stri- 
ated muscle-fiber.  The  light 
spaces  between  the  fibrils  may 
represent  the  sarcoplasm. 


broken  without  rupturing  the  sarcolemma,  we  may  see  this  sheath 
as  a  fine  glistening  line.      (Fig.  91.) 


126 


THE     TISSUES. 


The  fibrils  of  the  muscle-protoplasm  constitute  the  contractile 
part  of  the  muscle-fiber.  They  are  exceedingly  fine  and  extend  the 
entire  length  of  the  muscle-fiber,  and  consist  of  a  series  of  minute, 
rod-shaped  segments  with  attenuated  ends  (sarcous  elements),  united 
by  shorter  and  much  thinner  thread-like  bridges,  on  each  of  which 
there  is  found  a  small  granule  or  globule.  Their  structure  may  be 
expressed  in  the  form  of  a  diagram  (Fig.  92)  giving  the  view  of 
Rollett,  whose  account  has  here  been  followed. 

The  ultimate  fibrils  are  grouped  into  small  bundles  (0.3—0.5  [JL 

in  diameter),  forming  the  mus- 
cle-columns of  Kolliker.  In 
the  muscle-columns  the  fibrils 
are  so  placed  that  the  larger 
segments  fall  respectively  in 
the  same  plane.  (See  Fig.  92.) 
The  same  disposition  of  the 
fibrils  prevails  in  all  the  nu- 
merous muscle-columns  form- 
ing a  muscle-fiber,  and  all  the 
muscle-columns  bear  such  a 
relation  to  each  other  that 
the  larger  segments  of  the 
fibrils  fall  in  the  same  plane. 
The  semifluid,  interfibrillar 
substance,  the  sarcoplasm, 
penetrates  between  the  fibrils 
of  the  muscle-columns  and 
separates  these  from  each 
other  and  from  the  sarcolem- 
ma.  In  fresh  preparations  the 
substance  forming  the  fibrils 
appears  somewhat  darker  and 
dimmer,  while  the  sarcoplasm 
appears  clearer.  Accordingly, 
the  narrow  zone  formed  by 
the  larger  segments  of  the 
fibrils  appears  slightly  darker 
and  dimmer  than  the  zones 
in  the  regions  of  the  uniting 

bridges,  where  the  sarcoplasm  is  more  abundant  (see  Fig.  92),  giving 
these  zones  a  clearer  appearance.  This  gives  the  striated  muscle- 
fibers  their  characteristic  cross-striation.  The  sarcoplasm  is  found 
in  greater  abundance  between  the  muscle-columns  than  between 
the  fibrils  in  the  columns.  The  sarcoplasm  between  the  muscle- 
columns  appears  in  the  form  of  narrower  or  broader  lines,  parallel 
to  the  long  axis  of  the  muscle-fibers,  giving  the  cross-striated 
muscle-fiber  also  a  longitudinal  striation.  The  sarcoplasm  between 
the  muscle-columns  is  seen  to  best  advantage  in  cross-sections 


Sarcoplasm. 


Cohnheim's 

area. 


^  Sarcolemma. 


Sarcoplasm. 


Cohnheim's 
area. 


Sarcoplasm. 
-Fibrils. 
-Sarcolemma. 


Fig-  93-  —  Transverse  section  through 
striated  muscle-fibers  of  a  rabbit.  I  and  3, 
from  a  muscle  of  the  lower  extremity  ;  2, 
from  a  lingual  muscle  ;  X  9°°-  Technic  No. 
163.  In  2,  Cohnheim's  fields  are  distinct ;  in 
I,  less  clearly  shown  :  in  3,  the  muscle-fibrils 
are  more  evenly  distributed. 


MUSCULAR     TISSUE. 


127 


of  the  muscle-fiber.  Here  it  appears  in  the  form  of  a  network 
inclosing  the  muscle-columns.  Thus,  we  have  in  a  cross-section 
slightly  darker  areas,  the  cross-sections  of  the  muscle-columns, 
known  as  Colinkeiin's  fields  or  areas,  separated  by  the  network  of 
sarcoplasm.  (Fig.  93.) 

In  a  striated  muscle -fiber  the  darker  and  fainter  bands  (larger  seg- 
ments of  the  fibrils)  are  doubly  refracting,  anisotropic,  while  the  clearer 
bands  (sarcoplasm)  are  singly  refracting,  isotropic.  The  relative  group- 
ing of  the  two  unequally  refracting  substances  is,  however,  somewhat 
complicated,  a  condition  which  has  given  rise  to  much  discussion  as  to 
the  finer  structure  of  the  muscle-fiber.  It  should  be  remembered  that 
the  anisotropic  and  isotropic  substances  of  the  fiber  are  respectively  placed 
in  the  same  plane,  so  that  the 
cross -striation  of  the  entire  fiber 
is  fairly  regular.  The  thickness 
of  the  bands  varies  considerably, 
often  appearing  as  fine  lines.  In 
a  definite  segment  the  grouping 
is  very  regular,  and  the  structure 
of  such  a  segment  is  exactly 
repeated  throughout  the  entire 
length  of  the  fiber.  A  segment 
of  this  description  contains  in 
its  center  a  broad  disc  of  aniso- 
tropic substance — the  transverse 
disc  ((?)  (Fig.  94);  this  is  di- 
vided through  its  middle  by  a 
less  refractive  (isotropic)  narrow 
band,  known  as  the  median  disc 
of  Hensen  (/*).  Above  and 
below  the  transverse  disc  (  Q)  is 
a  disc  of  isotropic  substance 
(y);  these  in  turn  border  upon 
the  intermediate  discs  of  Krause 


Fig-  94-  —  Diagrams  of  the  transverse 
striation  in  the  muscle  of  an  arthropod  ;  to 
the  right  with  the  objective  above,  to  the  left 
with  the  objective  below  its  normal  focal  dis- 
tance (after  Rollett,  85):  Q,  Transverse  disc  ; 
A,  median  disc  (Hensen);  E,  terminal  disc 
(Merkel);  IV,  accessory  disc  (Engelmann);  J, 
isotropic  substance. 


(Z  ) .      There    are    consequently 

in  each  segment  or  muscle-casket 

four   discs — the    transverse  disc 

(  Q)  divided  into  two  parts  by 

the  median  disc  of  Hensen  (/>), 

with  above  and  below  the  two 

isotropic    discs    (./),  outside    of  which    lie    the    intermediate    discs  of 

Krause  (Z). 

One  of  the  best  objects  for  the  study  of  transverse  striation  is  the 
muscle  of  some  of  the  arthropods  (beetles).  Here  it  will  be  noticed  that 
the  disc  (  /)  is  separated  by  an  anisotropic  disc  through  its  center  into 
three:  (i)  an  isotropic  disc  (J")  ;  (2)  an  anisotropic  disc  (.#"),  the 
"accessory  disc"  of  Engelmann,  Krause' s  "transverse  membrane"; 
and  (3)  still  another  disc  of  anisotropic  substance  (£),  Merkel's  "ter- 
minal disc."  In  other  words,  the  number  of  discs  in  a  segmental  unit  is 
increased  to  six :  Q  divided  by  h,  twoy's,  two  JE's,  and  Z.  It  should 
be  remarked  here  that  all  the  doubly  refracting  substances  appear  as  light, 


128 


THE     TISSUES. 


and  the  singly  refracting  as  dark,  bands  when  the  objective  is  raised  just 
a  trifle  above  its  focal  distance.  The  contrary  is  the  case  on  lowering  the 
objective  to  a  point  just  below  its  focal  distance.  (Fig.  94.) 

In  figure  95  is  shown  a  portion  of  a  striated  muscle-fiber  of 
man  very  highly  magnified.  The  larger  and  darker  transverse  disc 
(Q)  formed  by  the  larger  segments  of  fibrils  is  divided  by  a  light 
line  (//),  Hensen's  median  disc  ;  the  clearer  band,  largely  sarcoplasm, 
is  divided  by  a  dark  line,  the  intermediate  disc  of  Krause  ;  this  falls 
in  the  plane  of  the  granules  on  the  fine  bridges  uniting  the  larger 
segments  of  the  fibrils. 

After  a  prolonged  treatment  with  98  °fo  alcohol  the  muscle -fibers 
of  the  water  beetle  {Hydrophilus 
piceus)  can  be  made  to  separate 
into  transverse  discs  (Rollet, 
85).  One  of  these  discs  would 
correspond  to  the  segment  Q, 
and  it  is  very  probable  that  this  is 
the  portion  which  has  long  been 
known  under  the  name  of  Bow- 


Fig.  95. — From  a  striated  muscle  of 
man ;  obtained  by  teasing  ;  X  1200. 
Technic  No.  166  :  h,  A  median  disc  lying 
in  the  transverse  disc  Q ;  z,  the  interme- 
diate disc  borders  above  and  below  on  the 
light  isotropic  discs. 


Fig.  96. — From  a  cross-section  through 
the  trapezius  muscle  of  man,  showing  dark 
fibers  rich  in  protoplasm,  and  light  fibers 
containing  very  little  protoplasm  (after 
Schaffer,  93,  II)  :  d,  Dark  fibers  ;  a,  light 
fibers  ;  b  and  ct  transitional  fibers  from  light 
to  dark. 


man's  disc.  Other  reagents,  as  weak  chromic  acid,  cause  a  separation 
of  the  muscle-substance  into  longitudinal  fibrils.  In  this  case  the  discs 
Q  are  split  up  longitudinally  into  a  number  of  very  small  columns 
which  were  at  one  time  regarded  as  the  primary  elements  of  the 
fiber  and  termed  by  Bowman  sarcous  elements. 

In  adult  skeletal  and  skin  muscle-fibers  of  mammalia  the  posi- 
tions of  the  nuclei  vary.  There  are  muscles  in  which  the  nuclei  are 
imbedded  in  the  sarcoplasm  between  the  muscle-columns  (so-called 
red  muscles,  as  the  semitendinosus  of  the  rabbit) ;  in  other  muscles 
they  lie  immediately  beneath  the  sarcolemma  (white  muscles,  as  the 
semimembranosus  of  the  rabbit ;  Ranvier,  89).  In  the  striated  mus- 


MUSCULAR    TISSUE.  129 

cle-fibers  of  the  lower  vertebrates  and  of  mammalian  embryos  the 
nuclei  lie  between  the  fibrillae,  or  muscle-columns.  The  red  muscle- 
fibers  are  rich  in  sarcoplasm,  and  the  fibrils  are  grouped  in  well- 
marked  and  large  muscle-columns  surrounded  by  sarcoplasm  which 
often  contains  granules  of  various  sizes,  the  interstitial  granules  of 
Kolliker,  often  especially  abundant  at  the  poles  of  the  nuclei.  The 
white  muscle-fibers  have  a  relatively  small  quantity  of  sarcoplasm. 
In  cross-sections  of  the  light  fibers  the  fibrils  show  as  fine  points,  not 
distinctly  grouped,  and  surrounded  by  the  homogeneous  sarcoplasm. 
Both  varieties  occur  in  almost  every  human  muscle,  and  the  relative 
number  of  each  varies  greatly  in  the  different  muscles  (Schaffer,  93, 
II,  Fig.  96). 

Muscles  with  transversely  striated  fibers  are,  with  the  exception 
of  those  of  the  heart,  subject  to  the  will  of  the  individual,  and 
are  characterized  by  a  rapid  contraction  in  which  the  anisotropic 
substance  increases  in  size  at  the  cost  of  the  isotropic  discs  ;  the 
former  appears  to  play  the  chief  role.  Besides  morphologic  dif- 
ferences, the  red  and  white  muscle-fibers  appear  to  possess  differ- 
ences of  a  physiologic  character,  in  that  the  contraction  in  the  red 


Fig.  97- — Branched,  striated  muscle-fiber  from  the  tongue  of  a  frog. 

variety  is  slower  than  that  in  the  white  (Ranvier,  80).  Only  the  stri- 
ated muscles  of  the  esophagus,  the  external  cremaster,  and  a  few 
others,  as  well  as  the  somewhat  differently  constructed  muscles  of 
the  heart,  are  involuntary. 

Transversely  striated  muscle-fibers  are  usually  unbranched. 
The  muscle-fibers  of  the  tongue  and  of  the  ocular  muscles  do,  how- 
ever, show  occasionally  communicating  branches  ;  the  same  are 
but  very  rarely  seen  in  other  muscles.  In  regions  where  striated 
muscle-fibers  terminate  under  the  epithelium,  as  in  the  tongue  and 
in  the  skin  of  the  face,  the  end  of  the  fiber  terminating  under  the 
epithelium  is  often  very  much  branched  ;  the  cross-striation  4nd 
nuclei  may  be  observed  in  the  finest  branches.  (Fig.  97.) 

Each  muscle-fiber  is  surrounded  by  a  thin  connective-tissue  en- 
velope, the  endomysium,  which  binds  them  into  primary  and  second- 
ary bundles,  the  muscle-fasciculi.  These  are  surrounded  by  a 
denser  sheath  of  similar  character,  the  perimysium.  The  muscle  is 
made  up  of  numerous  fasciculi,  all  bound  together  by  a  thicker  con- 
nective-tissue covering,  the  epimysium.  (Fig  98.) 

Blood-vessels  are  very  numerous  in  transversely  striated  mus- 
9 


130 


THE     TISSUES. 


Fig.  98. — Cross- section  of  rectus  abdominis  of  child,  as  seen  under  low  magnification. 


Muscle. 


1.1  (} 


«  » 5     4       0  M       ' 

llv  $  *   / '  °  1 

i"    ft*        )5      <    «  ; 
j-  vi  /«     /  tf     f 


f/ 

i:        -)      /  t 

:,l>f 


f'       a    I" 
ft       o° 


Tendon. 


V  V  N  ^  v     v  ^'  '   ^  ^f(    <      y      )>)(    , 

'''' '        ' 


Fig.  99- — Part  of  a  longitudinal  section  through  the  line  of  junction  between  muscle 
and  tendon  ;  X  I5°-  At  the  line  where  the  tendon-fibrils  join  the  sarcolemma  (a),  the 
nuclei  of  the  muscle  are  very  numerous.  Sublimate  preparation. 


MUSCULAR     TISSUE. 


cular  tissue.  They  form  a  capillary  network  with  elongated  meshes, 
the  cross-branches  of  which  sometimes  show  swellings  in  the  red 
muscles  (Ranvier,  80).  The  smallest  veins  are  relatively  large  and 
possess  numerous  valves. 

At  its  junction  with  tendon  the  muscle-fiber  with  its  sarcolemma 
is  rounded  off  into  a  blunt  point,  the  fibrils  of  the  tendon  being 
cemented  to  the  sarcolemma. 

The  longitudinal  growth  of  muscle-fibers  takes  place  principally 
at  the  distal  ends  of  the  fibers,  at  which  point  their  nuclei  are  numer- 
ous. (Fig.  99,  at  a.)  Schaffer  (93,  II)  has  recently  suggested  that 
there  is  a  formative  tissue  between  the  tendon  and  muscle-substance, 
from  which,  on  the  one  hand,  muscle-fibers  are  developed,  and,  on 
the  other  hand,  connective-tissue  fibrils  and  cells  are  formed. 

As  recent  investigations  have  shown,  the  development  of  muscle 
continues  throughout  the  life  of  the  individual.  Muscular  tissue  is 


--   Nucleus. 


Contractile 
substance. 


Contractile 
substance. 


—   Nucleus. 


Fig.   100.  Fig.  101. 

Longitudinal  and  cross-section  of  muscle-fibers  from  the  human  myocardium,  hard- 
ened in  alcohol ;  X  640.  The  muscle  cells  in  the  longitudinal  section  are  not  sharply 
defined  from  each  other,  and  appear  as  polynuclear  fibers  blending  with  each  other. 
Between  them  lie,  here  and  there,  connective-tissue  nuclei. 

consequently  to  be  regarded  as  in  a  perpetual  stage  of  transition, 
the  destruction  and  compensatory  reproduction  of  its  elements  going 
on  hand  in  hand.  Its  destruction  is  ushered  in  by  a  process  which 
can  be  compared  to  a  physiologic  contraction.  Nodes  or  thickened 
rings  are  formed,  and  at  these  points  the  muscle-substance  separates 
into  fragments  with  or  without  nuclei  (sarcolytes),  which  are  then 
absorbed,  in  most  cases  without  phagocytic  aid.  This  loss  of  sub- 
stance is  replaced  by  new  elements  developed  from  the  free  sarco- 
plasm,  which  is  characterized  by  rapid  growth  and  increase  in  the 
number  of  its  nuclei.  The  result  is  that  new  elements  are  formed 
which  have  been  called  rnyoblasts.  The  process  by  which  myo- 
blasts  are  changed  into  the  finished  muscle-fibers  is  exemplified  in 
the  embryonal  type  of  development  of  the  tissue. 


132  THE     TISSUES. 

CARDIAC  MUSCLE-CELLS. 

The  muscle-cells  of  the  heart  differ  in  structure  from  the  ordi- 
nary type  of  transversely  striated  muscle-fibers.  The  heart  muscle- 
cells  are  short,  irregularly  oblong  cells,  often  branched,  possess  no 
sarcolemma,  and  have  one,  occasionally  two,  centrally  placed  nuclei. 
In  the  smaller  muscle-cells  a  cross-section  often  shows  an  arrange- 
ment of  the  fibrils  radiating  from  the  axis.  The  heart  muscle-cells 
are  cemented  end  to  end  to  form  anastomosing  heart  muscle-fibers  ; 
these  are  arranged  in  bundles  or  in  the  form  of  a  network. 

The  muscle-cells  of  the  so-called  fibers  of  Purkinje  lie  immediately 
beneath  the  endocardium,  and  are  remarkable  in  that  their  proto- 
plasm is  only  partially  formed  of  transversely  striated  substance,  and 
that  only  at  their  periphery.  Such  cells  are  found  in  great  numbers 
in  some  animals  (sheep),  but  rarely  in  man.  Heart  muscle  has  a 
rich  blood  supply,  which  will  be  considered  more  fully  when  the 
heart  is  discussed  as  an  organ. 

For  the  nerve-endings  in  smooth  and  striated  muscle-fibers  see 
the  chapter  on  Nervous  Tissues. 

TECHNIC 

161.  Fresh,  striated  muscle-fibers  may  be  isolated  by  teasing  them  in 
an   indifferent   fluid  (vid.  T.  13).      After  a  short  time  the  sarcolemma 
may  separate  as  a  very  fine  membrane.      If  a  freshly  teased  muscle  be 
placed  in  a  cold  saturated  solution  of  ammonium  carbonate,    the  sar- 
colemma will  become  detached  in  places  within  five  minutes  (Solger, 
89,  III). 

162.  Striated  muscle-fibers  may  be  examined  in  an  extended  condi- 
tion by  placing  an  extremity  in  such  a  position  as   to  stretch  certain 
groups  of  muscles.     A  subcutaneous  injection  of  0.25-0.5  c.c.  of  a  ify 
osmic  acid  solution  is  then  made.    The  acid  penetrates  between  the  fibers 
and  fixes  them.     Pieces  of  muscle  are  then  cut   out  and  washed  in  dis- 
tilled water.     Teased  fibers,  even  if  not  stained,  will   show  the  stria- 
tion   plainly  if  mounted  in  glycerin.      Muscles  thrown  into  a  state  of 
tetanic  contraction  by  electric  stimulation  may  also  be  fixed  in  this  state 
and  later  examined. 

163.  Cross-sections  of  muscles,   extended  and  fixed  in  osmic  acid, 
also  show  the  relation  of  the  fibrils  to  the  sarcoplasm  (Cohnheim's  fields). 
A  remarkable  quantity  of  sarcoplasm   in  proportion  to  the  number  of 
fibrils  is  seen,  for  instance,  in  the  muscles  which  move  the  dorsal  fin  of 
hippocampus ;  among  the  mammalia  a  similar  condition  is  found  in  the 
pectoral  muscles  of  the  bat  (Rollett,  89). 

164.  In  the  muscles  of  all  adult  vertebrates  (except  the  mammalia) 
the  nuclei   lie  between  the  fibrils.      In  young  mammalia  they  also  have 
this  position,  but  in  the  adult  animals  only  the  nuclei  of  red  muscles 
are  found  between  the  fibrillse  ;  in  all  other  muscles  the  nuclei  are  under 
the  sarcolemma. 

165.  The  fibrillar  structure  of  muscle-fibers  can  be  seen  by  teasing  old 
alcoholic  preparations,  or  tissue  treated  with  weak  chromic  acid  (0.1%) 
or  one  of  its  salts. 


THE    NERVOUS    TISSUES.  133 

166.  In  alcoholic    preparations   of  mammalian   muscle,    the    cross- 
striation  is  clearly  seen,  and  is  intensified  by  staining  with  hematoxylin. 
This  stain  colors  everything  anisotropic  in  the  muscle,  but  does  not  affect 
the  remaining  structures.      Similar  results  may  be  obtained  with  other 
stains,  such  as  basic  anilin  dyes,  but  not  with  the  same  precision  as  with 
hematoxylin. 

167.  A  certain  species  of  beetle  (Hydrophilns)  is  admirably  adapted 
for  the  study  of  the  finer  details  of  striation.    The  beetle  is  first  wiped  dry 
and   then   immersed  alive  in   93%    alcohol.      On   examining  in   dilute 
glycerin  after  from    twenty-four  to  forty-eight    hours,   the  substance  of 
its  muscles  will  show  disintegration  into  Bowman's  discs  (vid.  p.  128). 
The    latter   swell    up    in    acids   and   are    finally   dissolved,   as   may   be 
seen,  by  adding  a  drop  of  formic  acid  to  a  specimen  prepared  as  above 
(Rollet,  85). 

168.  In  order  to  study  the  relation  of  muscle  to  tendon,  small  mus- 
cles with  their  tendons  are  put  into  a  35%  potassium  hydrate  solution  for 
a  quarter  of  an  hour,  after  which  the  specimen  is  placed  upon  a  slide  and 
teased  at  the  line  of  junction  of  the  two  tissues.     This  will  separate  the 
muscle-fibers  from  their  respective  tendon-fibrils  (Weismann). 

169.  Similar  results  may  be  obtained  by  immersing  a  frog  in  water 
at  a  temperature  of  55°  C.,  in  which  the  animal  soon  dies  with  muscles 
perfectly  rigid.     As  soon  as  the  water  begins  to  cool   (one-quarter  hour) 
the  frog  is  removed  and  a  small  piece  of  its  muscle  cut  out  and  teased  in 
water  on  a  slide  (Ranvier). 

170.  Cardiac  muscle -cells  are  isolated  by  maceration  for  twenty -four 
hours  in  a  20%  solution  of  fuming  nitric  acid  (potassium  hydrate  with  a 
specific  gravity  of  1.3  will  do   the  same  in  one-half  or  one  hour).     The 
margins  of  the  cells  may  be  brought  more  clearly  into  view  by  placing 
pieces  of  heart  muscle  for  twenty-four  hours  in  a  0.5%  aqueous  solution 
of  silver  nitrate  and  then  cutting  into  sections. 

171.  Isolated  fibers  of  Purkinje  are  obtained   by  immersing  pieces 
of  endocardium  (0.5   mm.   in  size)   in  33%  alcohol  and  then   teasing 
them  on  a  slide.     The  sheep's  heart  is  especially  well  adapted  for  this 
purpose. 

172.  Nonstriated  muscle-fibers  are  isolated  in  the  same  way  as  heart 
muscle.      In   thin   cross-sections  (under   5  ^  in   thickness)   of  intestinal 
muscle,  preferably  of  a  cat,  fixed  in  osmic  acid,  the  intercellular  bridges 
may  be  seen  here  and  there  between  the  fibers. 


D.  THE  NERVOUS  TISSUES* 

The  entire  nervous  system,  peripheral  as  well  as  central,  is  com- 
posed of  cells  possessing  one  or  many  processes.  These  cells 
develop  early  in  embryonic  life  from  certain  ectodermal  cells  (nenro- 
blasts)  of  the  neural  canal,  which  is  formed  by  a  dorsal  invagination 
of  the  ectoderm.  The  neuroblasts  soon  develop  processes, — many 
of  them  in  loco,  others  only  after  wandering  from  the  neural  canal. 

The  processes  of  the  nerve-cells  are  of  two  kinds:  (i)  un- 
branched  processes  having  a  nearly  uniform  diameter  throughout, 


134  THE   TISSUES. 

with  lateral  offshoots  known  as  collateral  branches  ;  these,  as  we 
shall  see,  generally  form  the  central  part  of  a  nerve-fiber,  and  are 
known  as  neuraxes  (Deiters'  processes,  axis-cylinder  processes, 
neurites,  neuraxones  or  axones) ;  and  (2)  processes  which  branch 
soon  after  leaving  the  cell-body  and  break  up  into  many  smaller 
branches  ;  these  are  the  dendrites,  or  protoplasmic  branches.  In  the 
spinal  ganglia  and  the  homologous  cranial  ganglia  these  morpho- 
logic differences  in  the  processes  are  not  observed,  the  neuraxis  and 
the  dendrites  of  each  presenting  essentially  the  same  structure. 

To  the  entire  nerve-cell,  cell-body  and  processes  the  term 
neurone (Waldeyer,  91)  has  been  applied;  neura  (Rauber),  or  neu- 
rodendron  (Kolliker,  93). 

The  neuraxes  of  many  neurones  attain  great  length.  Those  of 
some  of  the  neurones,  the  cell-bodies  of  which  are  situated  in  the 
lower  part  of  the  spinal  cord,  extend  to  the  foot.  In  other  regions 
neuraxes  nearly  as  long  are  to  be  found,  and  in  the  majority  of  neu- 
rones the  neuraxes  terminate  some  distance  from  the  cell-body.  It  is 
therefore  manifestly  impossible  in  the  majority  of  cases  to  see  a  neu- 
rone in  its  entirety.  Usually,  only  a  portion  of  one  can  be  studied 
in  any  one  preparation.  Consequently,  the  more  detailed  descrip- 
tion* which  follows  will  deal  with  the  neurone  in  this  fragmentary 
manner.  The  cell-bodies  of  the  neurones,  to  which  the  term 
"  nerve-cells  "  or  "  ganglion  cells  "  is  usually  restricted,  the  den- 
drites and  neuraxes,  often  forming  parts  of  nerve-fibers,  and  their 
mode  of  terminating,  will  receive  separate  consideration. 


NERVE-CELLS,  OR  GANGLION  CELLS ;  THE  CELL-BODIES  OF 

NEURONES, 

The  cell-bodies  of  nerve-cells  are  usually  large.  The  bodies  of 
the  motor  neurones  of  the  human  spinal  cord  measure  75  to  150  //, 
their  nuclei  45  //,  and  their  nucleoli  1 5  /2.  The  smallest  nerve-cells, 
the  neurones  of  the  granular  layer  of  the  cerebellum,  are  4  to  9  p  in 
diameter.  The  protoplasm  of  nerve-cells  shows  a  distinct  fibrillar 
structure  and  the  fibrils  may  be  followed  into  the  processes.  (Fig. 
1 02.)  Their  nuclei  are  also  large,  with  very  little  chromatin,  but  as 
a  rule  are  supplied  with  a  large  nucleolus. 

After  treatment  by  certain  special  methods,  the  protoplasm  of 
the  ganglion  cells  shows  granules  or  groups  of  granules  which  show 
special  affinity  to  certain  stains,  consequently  known  as  chromato- 
phile  granules  ;  these  are  densely  grouped  around  the  nucleus,  so 
that  the  cell-body  shows  an  inner  darker  and  an  outer  lighter  por- 
tion. These  chromatophile  granules,  also  spoken  of  as  tigroid 
granules  or  as  the  tigroid  substance,  as  a  rule  are  not  arranged  in 
concentric  layers,  but  lie  mostly  in  groups,  giving  to  the  protoplasm  a 
mottled  or  reticular  appearance.  In  the  cells  of  the  anterior  horns 
(man,  ox,  rabbit)  the  granules  join  to  form  flakes,  which  are  also 
more  numerous  in  the  region  of  the  nucleus.  In  all  cases  the 


THE    NERVOUS    TISSUES.  135 

granules  or  flakes  are  continued  into  the  dendrites  of  the  cell.  Here 
they  change  their  shape  into  long  pointed  rods,  with  here  and  there 
nodules,  which  are  probably  the  chief  causes  of  the  varicosities  so 
often  seen  in  dendrites  (Golgi's  method).  The  cell  usually  has  a 
clear,  nongranular  peripheral  border  (not  a  membrane),  and  in  the 
case  of  large  cells  there  is  a  similar  area  around  the  nucleus,  the 
inner  border  of  which  belongs  to  the  nuclear  membrane.  H.  Held 
has  found  that  the  chromatophile  granules  are  brought  out  by  treat- 
ment with  alcohol  and  acid  fixing  fluids,  but  not  in  alkaline  or  neu- 
tral. They  appear,  according  to  the  treatment,  as  fine  or  coarse 
granules.  They  can  not  be  seen  in  fresh  nerve-cells.  He  conse- 
quently regards  them  as  artefacts — precipitations  of  the  protoplasm 
due  to  reagents  (yid.  A.  Fischer,  T.  124).  At  its  junction  with  the 
cell  the  neuraxis  spreads  out  into  a  cone  which  is  entirely  free  from 
granules,  and  apparently  fitted  into  a  depression  in  the  granular 
substance  of  the  cell  (implantation  cone). 

The  cellular  substance  between  the  chromatophile  granules  con- 
sists also  of  very  fine,  highly  refractive  granules,  which  appear  to  be 
arranged  in  a  reticulum  surrounding  the  chromatophile  granules 

Nucleus.  wr*sm—uto^  . <  NucleoluS. 


-  Fibrillar  structure. 
Medullary  sheath. 


Fig.  102. — Bipolar  ganglion  cell  from  the  ganglion  acusticum  of  a  teleost  (longi- 
tudinal section).  The  medullary  sheath  of  the  neuraxis  and  dendrite  is  continued  over  the 
ganglion  cell ;  X  800.  Technic  No.  175. 

(yid.  Nissl,  94,  and  v.  Lenhossek,  95),  and  the  recent  observations 
of  Apathy  and  Bethe  make  it  very  probable  that  in  the  intergranular 
substance  of  the  protoplasm  of  the  nerve-cell  there  exist  very  fine 
fibrils  which  may  be  traced  into  the  processes  of  the  cell.  It  requires, 
however,  further  observation  before  more  positive  statements  may 
be  made  concerning  them. 

Besides  the  granules  above  mentioned,  and  which  are  revealed 
by  special  methods,  there  are  found  in  the  protoplasm  of  many  of 
the  larger  nerve-cells  pigment  granules  of  a  yellow  or  brown  color 
which  stain  black  with  osmic  acid. 

The  dendrites  are  usually  relatively  thick  at  their  origin,  but 
gradually,  as  a  result  of  repeated  divisions,  taper  until  their  widely 
distributed  arborescent  endings  appear  as  minute  threads  of  widely 
different  shapes.  When  treated  by  certain  methods,  they  present 
uneven  surfaces  studded  with  varicosities  and  nodules,  in  contradis- 
tinction to  the  neuraxes,  which  are  smooth  and  straight.  Their  ter- 
minal branches  end  either  in  points  or  in  small  terminal  thickenings. 
The  groups  of  terminal  end-branches  of  a  dendrite  (also  of  a  neur- 
axis) are  known  as  telodendria  (Rauber),  or  end-branches.  The 


136 


THE    TISSUES. 


branches  of  the  dendrites  form  a  dense  feltwork,  which,  together 
with  the  cell-bodies  of  the  neurones  and  with  other  elements  to  be 
described  later,  constitute  the  gray  substance  (gray  matter)  of  the 
brain  and  spinal  cord. 

All  neurones,  with  possibly  a  few  exceptions,  possess  only  a 
single  neuraxis.  Neurones  without  a  neuraxis  have  never  been 
found  in  vertebrates.  The  neuraxis  usually  arises  from  a  cone- 
shaped  extension  of  the  cell-body  free  from  chromatophile  granules, 
the  implantation  cone,  more  rarely  from  the  base  of  one  of  its 
dendrites,  or  from  a  dendrite  at  some  distance  from  the  cell-body. 
Its  most  important  characteristics  are  its  smooth  and  regular 
contour  and  its  uniform  diameter.  At  some  distance  from  the  cell- 
body,  usually  near  its  termination,  now  and  then  in  its  course,  a 
neuraxis  may  divide  into  two 
equal  parts.  Golgi  (94)  called 
attention  to  the  fact  that  the  neu- 
raxes  of  certain  neurones  (Pur- 
kinje's  cells  in  the  cerebellum, 
pyramidal  cells  of  the  cerebral 
cortex,  and  certain  cells  of  the 
spinal  cord)  give  off  lateral  pro- 
cesses, the  collateral  branches. 


_  Nucleus. 


Implanta- 
tion cone. 


Fig.  103. — Chromatophile  granules  of 
a  ganglion  cell  from  the  Gasserian  ganglion 
of  a  teleost :  a,  Nucleus  ;  b,  implantation 


Fig.  104. — Nerve-cell  from  the  ante- 
rior horn  of  the  spinal  cord  of  an  ox, 
showing  coarse  chromatophile  flakes. 


Two  types  of  cell  are  recognized  according  to  the  disposition  of 
their  neuraxes  :  In  the  first  the  neuraxis  is  continued  as  a  nerve- 
fiber  ;  in  the  second  and  rarer  type  it  does  not  long  preserve  its 
.independence,  nor  is  it  continued  as  a  nerve-fiber,  but  soon  breaks 
up  into  a  complicated  arborization,  the  neuropodia  of  Kolliker  (93). 
The  latter  type  of  cell  occurs  in  the  cortex  of  the  cerebrum  and 
cerebellum  and  in  the  gray  matter  of  the  spinal  cord.  The  cells  of 
the  two  types  can  be  simply  described  as  having  long  (type  I)  or 
short,  branched  neuraxes  (type  II).  The  neuraxes  of  the  cells  of 
type  I  possess  the  collateral  branches  which  end  in  small  branching 
tufts. 

In  its  simplest  form,  a  neurone  consists  of  a  cell-body  and  a  neu- 
raxis with  its  telodendrion.  In  more  complicated  types  one  or  several 


THE    NERVOUS    TISSUES. 


137 


dendrites  may  be  present,  as  also  collaterals  from  the  neuraxis,  and 
in  rare  cases  even  several  neuraxes.  According  to  the  number  of 
its  processes,  a  ganglion  cell  is  known  as  unipolar,  bipolar,  or 
multipolar. 


— Dendrite. 


Neuraxis. 


Neuraxis. 


Dendrite. 


Fig.  105. — Motor  neurones  from  the  anterior  horn  of  the  spinal  cord  of  a  new-born  cat. 

Chrome-silver  method. 

Although  neurones  present  a  great  variety  of  morphologic  dif- 
ferences,— large  and  variously  shaped  cell-bodies  or  small  ones 
scarcely  larger  than  the  nucleus  ;  large  and  numerous  dendrites  or 


s-  Telodendrion. 


Dendrite. 


Cell-body. 


—  Neuraxis. 


Fig.  106. — A  nerve-cell  with  branched  dendrites  (Purkinje's  cell),  from  the  cerebellar 
cortex  of  a  rabbit ;  chrome-silver  method  ;  X  I2S- 

few  and  less  conspicuous  ones, — and  although  these  various  forms 
are  widely  distributed  and  intermingled  in  the  different  parts  of  the 
nervous  system,  yet  in  many  regions  there  are  found  nerve-cells  of 
fixed  and  characteristic  morphologic  appearance,  which  would 


138  THE    TISSUES. 

enable  a  determination  of  their  source.  A  few  of  the  most  charac- 
teristic types  are  here  figured  and  may  receive  brief  consideration. 
In  the  anterior  horn  of  the  spinal  cord  are  found  large,  multipolar 
neurones  (motor  neurones),  with  numerous  dendrites,  which  termi- 
nate after  repeated  branching  in  the  neighborhood  of  the  cell-body, 
while  the  neuraxis  with  its  collateral  branches  proceeds  from  the 
cell-body  and  becomes  a  part  of  a  nerve-fiber.  (Fig.  105.) 

In  the  cerebellum  are  found  large  neurones,  discovered  by  Pur- 
kinje,  and  known  as  Purkinje's  cells,  with  flask-shaped  cell-body,  from 
the  lower  portion  of  which  arises  a  neuraxis  with  collateral  branches, 


b  -- 


Branching  of  a 

dendrite. 


Neuraxis  and 

collaterals. 


Fig.  107. — Pyramidal  cell  from  the  cerebral  cortex  of  man  ;  chrome-silver  method  : 
a,  b,  c,   Branches  of  a  dendrite. 

from  the  upper  portion  one  or  two  very  large  and  typic  dendrites 
the  smaller  branches  of  which  are  beset  with  irregular  granules. 
(Fig.  1 06.) 

In  the  cortex  of  the  cerebrum  occur  large  neurones,  each  with  a 
cell-body  the  shape  of  a  pyramid  (pyramidal  cell  of  the  cerebral 
cortex),  from  the  apex  of  which  arises  one  large  dendrite,  and  from 
angles  at  the  base,  or  from  the  sides  of  the  cell-body,  several  smaller 
dendrites.  The  neuraxis  arises  from  the  base  directly  or  from  one 
of  the  basal  dendrites.  (Fig.  107.) 


THE    NERVOUS   TISSUES.  139 

In  figure  108  is  shown  a  neurone  with  relatively  small  cell-body 
and  short  dendrites,  from  the  granular  layer  of  the  human  cere- 
bellum. 

The  function  of  the  dendrites  has  given  rise  to  considerable  dis- 
cussion. Golgi  and  his  school  regard  them  as  the  nutrient  roots  of 
the  cell,  a  theory  which  is  opposed  by  Ramon  y  Cajal  (93, 1 ),  van 
Gehuchten  (93,  I),  and  Retzius  (92,  II).  According  to  the  latter, 
all  the  processes  of  the  nerve-cell  are  analogous  structures  ;  they 
pass  out  from  a  sensitive  element,  and  probably  have  a  correspond- 
ingly uniform  function. 

In  the  spinal  ganglia  and  the  homologous  cranial  ganglia,  are 
grouped  the  cell-bodies  of  neurones  (peripheral  sensory  neurones, 
peripheral  centripetal  neurones)  which  differ  in  many  respects  from 
those  above  described.  In  the  peripheral  sensory  neurones  the 


—  Neuraxis. 


—  Telodendrion. 

--  Nucleus. 


Fig.  108. — Nerve-cell  with  dendrites  Fig.  109. — Ganglion  cell  with  a  pro- 
ending  in  claw-like  telodendria  ;  from  the  cess  dividing  at  a  (T-shaped  process);  from 
granular  layer  of  the  human  cerebellum  ;  a  spinal  ganglion  of  the  frog ;  X  23°- 
chrome-silver  method  ;  XIIO«  Technic  No.  178. 

neuraxes  and  dendrites  have  essentially  the  same  structure,  both 
forming  part  of  a  nerve-fiber.  From  a  relatively  large,  nearly  round, 
oval,  or  pear-shaped  cell-body  there  arises  a  single  process,  which, 
at  a  variable  distance  from  the  cell-body,  divides  into  two  branches 
forming  a  right  or  obtuse  angle  with  the  single  process  (T-shaped 
or  Y-shaped  division  of  Ranvier,  78).  Both  of  these  branches  form 
the  central  axis  of  a  nerve-fiber ;  one  of  the  branches  passing  as  a 
nerve-fiber  to  the  spinal  cord  or  brain,  as  the  case  may  be  ;  the  other 
forming  a  nerve-fiber  which  passes  to  the  periphery.  (Figs.  109  and 
no.) 

The  ganglion  cells  of  the  spinal  ganglia  and  homodynamic 
structures  of  the  brain  are  therefore  apparently  unipolar  cells,  but, 
as  Ranvier  has  shown,  their  processes  are  subject  to  a  T-shaped  or 
Y-shaped  division.  The  branches  going  to  the  periphery  are  re- 


140 


THE     TISSUES. 


garded  as  dendrites,  the  others  as  neuraxes.     As  to  the  significance 
to  be   attached  to  the  single  process,  the  theory  of  v.  Lenhossek 


Fig.  IIO. — Ganglion  cell  from  the  Gasserian  ganglion  of  a  rabbit ;  stained  in  methylene- 

blue  (infra  vitani). 

(94,  I)  that  it  represents  an  elongated  portion  of  the  cell,  and  that 
therefore  the  origin  of  the  dendrite  and  that  of  the  neuraxis  are  in 
this  case  close  together,  is  very  plausible.  In  the  embryo  these 
ganglion  cells  are  at  first  bipolar,  a  process  arising  from  each  end 

of  a  spindle-shaped  cell ;  as  de- 
velopment proceeds,  the  two  pro- 
cesses approach  each  other  and 
ultimately  arise  from  a  drawn-out 
portion  of  the  cell  -  body,  the 
single  process.  (Fig.  ill.) 

The  sympathetic  ganglia  are 
composed  mainly  of  the  cell- 
bodies  and  dendrites  (also  some 
structures  to  be  mentioned  later) 
of  neurones  of  the  sympathetic 
nervous  system.  In  nearly  all 
vertebrates,  and  with  but  few  ex- 
ceptions in  any  one  ganglion, 
these  neurones  are  multipolar  and 


Fig.  in. — Three  ganglion  cells  from 
a  spinal  ganglion  of  a  rabbit  embryo.  The 
cells  are  still  bipolar.  Their  processes 
come  together  in  later  stages,  and  finally 
form  the  T-shaped  structure  seen  in  the 
adult  animal  ;  chrome  -  silver  method  ; 


resemble     morphologically    the 

multipolar  ganglion  cells  of  the  anterior  horn  of   the  spinal  cord, 
though  they  are  somewhat  smaller.   In  the  cell-body  there  may  be  ob- 


THE    NERVOUS   TISSUES.  14! 

served  fine  chromatophile  granules  and  a  large  nucleus  and  nucleolus. 
From  the  cell-body  there  proceed  a  varying  number  of  dendrites 
which  branch  and  rebranch  and  terminate,  as  a  rule,  near  the  cell- 
body,  forming  plexuses  in  the  ganglia.  The  neuraxis  arises  either 
directly  from  the  cell-body  from  an  implantation  cone,  or  from  one  of 
the  dendrites  at  a  variable  distance  from  the  cell-body.  (Fig.  112.) 
In  nearly  all  ganglia  a  few  unipolar  or  bipolar  cells  are  to  be  found. 
In  the  sympathetic  nervous  system  of  amphibia  the  sympathetic 
neurones  are  unipolar  ;  the  single  process  present  is  the  neuraxis. 

A  most  important  result  of  the  more  recent  investigations  on  the 
nervous  system  is  the  theory  of  the  independence  of  the  neurone. 
Each  neurone  develops  from  a  single  cell  (neuroblast),  and  func- 
tionates as  an  independent  cell  under  physiologic  and  pathologic 
conditions.  Only  very  rarely  has  any  direct  connection  between 
two  neighboring  neurones  been  demonstrated,  so  rarely  that  the 


Fig.  112. — Neurone  from  inferior  cervical  sympathetic  ganglion  of  a  rabbit ;    methylene- 

blue  stain. 

scattered  observations  at  hand  do  not  vitiate  the  above  statement. 
Recent  investigations  have,  however,  shown  that,  while  a  neurone  is 
a  distinct  anatomic  unit,  it  is  always  found  associated  with  other 
neurones.  Nowhere  in  the  body  of  a  vertebrate  does  one  find  a 
neurone  completely  disconnected  from  other  neurones.  This  asso- 
ciation of  one  neurone  with  one  or  several  other  neurones  is  always 
effected  by  a  close  contiguity  existing  between  the  telodendria 
(end-branches)  of  the  neuraxis  of  one  neurone  with  the  cell -body  or 
dendrites  of  one  or  several  other  neurones.  The  telodendrion  of 
the  neuraxis  of  one  neurone  may  form  a  feltwork  inclosing  the  cell- 
body  of  one  or  several  neurones,  forming  structures  known  as 
terminal  baskets  or  end-baskets,  or  the  end  ramifications  of  the 
neuraxis  of  a  neurone  may  come  in  very  close  proximity  to  the 
end-branches  of  the  dendrites  of  one  or  several  neurones.  By  this 
contiguity  of  the  telodendria  of  the  neuraxis  of  one  neurone  with 


142 


THE     TISSUES. 


the  cell-bodies  or  the  dendrites  of  other  neurones,  they  are,  without 
losing  their  identity,  linked  into  chains,  so  that  a  physiologic  conti- 
nuity exists  between  them.  In  such  neurone  chains  the  dendrites 
are  regarded  as  cellulipetal,  transmitting  the  stimulus  to  the  cell  ;  the 
neuraxes  as  cellulifugal,  transmitting  the  impulse  imparted  by  the 
cell  to  the  motor  nerve-endings  or  central  organs  (Kolliker,  93). 
The  entire  nervous  system  may  therefore  be  said  to  be  made 
up  of  such  neurone  chains,  the  complexity  of  which  varies 
greatly  according  to  the  number  of  neurones  which  enter  into 
their  construction.  This  subject  will  be  considered  more  fully 
in  a  chapter  on  the  nervous  system. 


Fibrils  of  axial 
cord. 


•  Neurilemma. 


Segment  of 
Lantermann. 


THE  NERVE-FIBERS. 

The  neuraxes  of  the  cells  of  type   I,  and  the  dendrites  of  the 
peripheral  sensory  neurones  (spinal  ganglia  and  homologous  cranial 

ganglia),  form  the  chief  elements  in  all  the 
nerve-fibers.  In  the  nerve-fibers  they  pos- 
sess a  distinctly  fibrillar  structure.  The 
fibrils  composing  them,  the  axis-fibrils,  are 
imbedded  in  a  semifluid  substance,  the 
neuroplasm  (Kupffer,  83,  II)  the  whole 
being  surrounded  by  a  very  delicate 
membrane,  the  axolemvia.  In  the  nerve- 
fibers,  the  axis-fibrils  and  the  neuroplasm 
form  axial  cords  which  are  surrounded 
by  a  special  membrane  or  membranes, 
the  presence  or  absence  of  which  serves 
as  a  basis  for  a  classification  of  nerve- 
fibers.  Two  kinds  are  distinguished, 
medullated  and  nonmedullated  nerve  - 
fibers. 

In  medullated  nerve-fibers,  the  axial 
cords  (neuraxes  of  cells  of  type  I,  and 
dendrites  of  spinal  ganglion  cells)  are  sur- 
rounded by  a  highly  refractive  substance 
very  similar  to  fat,  which  is  blackened 
in  osmic  acid,  the  so-called  medullary  or  myelin  sheath.  In  a  fresh 
condition  this  sheath  is  homogeneous,  but  soon  changes  and  presents 
segments  separated  from  each  other  by  clear  fissures.  These  seg- 
ments vary  in  size  and  are  known  as  "  Schmidt-Lantermann-Kuhnt's 
segments."  On  boiling  in  ether  or  alcohol  the  entire  medullary 
sheath  of  a  nerve-fiber  does  not  dissolve,  but  a  portion  is  left  in  the 
shape  of  a  fine  network  which  is  not  affected  by  exposure  to  the 
action  of  trypsin.  From  the  latter  circumstance  it  has  been  thought 
that  this  network  consists  of  a  substance  very  similar  to  horn,  and 
is  therefore  known  as  neurokeratin  (horn-sheath,  Ewald  and  Kiihne). 
On  burning  isolated  neurokeratin,  an  odor  exactly  like  that  of  burn- 


Fig.  113. — Longitudinal 
section  through  a  nerve- fiber 
from  the  sciatic  nerve  of  a 
frog;  X830-  Technic  No. 
175- 


THE    NERVOUS    TISSUES. 


143 


ing  horn  is  given  off.  It  is  thought  that  the  meshes  of  this  neuro- 
keratin  network  contain  the  highly  refractive  substance  similar  to 
fat,  composing  the  greater  portion  of  the  medullary  sheath.  The 
medullary  sheath  is  interrupted  at  intervals  of  from  80  to  900  //,  the 
constrictions  thus  formed  being  known  as  the  nodes  of  Ranvier.  The 
smaller  the  fiber,  the  less  the  distance  between  the  nodes.  In  a  fiber 
with  a  diameter  of  2  jj.  the  internodal  segments  are  usually  about 
90  fj.  in  length. 

In  peripheral  nerves  the  medullary  sheath  is  in  its  turn  sur- 
rounded by  a  clear,  structureless  membrane,  the  neurilemma  or 
sheath  of  Schwann.  Nerve-fibers  contain  here  and  there  relatively 
long,  oval  nuclei  (neurilemma-nuclei)  which  are  surrounded  by  a 
small  quantity  of  protoplasm,  and  are  situated  in  small  excavations 
between  the  neurilemma  and  the  medullary  sheath.  In  the  higher 
vertebrates  a  single  nucleus  is  found  midway  between  each  two 


Connective  .„_ 
tissue. 


Fibrils  of  axial 
cord. 

Medullary 
sheath. 


Fig.  1 14. — Transverse  section  through  the  sciatic  nerve  of  a  frog  ;  X  ^2O-  Technic 
No.  175  :  At  a  and  b  is  a  diagonal  fissure  between  two  Lantermann's  segments  ;  as  a 
result,  the  medullary  sheath  here  appears  double.  (Compare  Fig.  113.) 

nodes  ;  in  the  lower  vertebrates  (fishes)  several  scattered  nuclei 
(5-16)  may  be  found  in  each  internodal  segment.  At  the  nodes, 
where  the  medullary  sheath  is  interrupted,  the  neurilemma  is 
thickened  and  contracted  down  to  the  axial  cord  (contraction-ring). 

Just  beneath  the  contraction-ring,  Ranvier  found  that  the  axis- 
cylinder  presents  a  slight,  biconic  swelling  (renflement  bicbnique). 
Thus  the  sheath  of  Schwann  represents  a  continuous  tube  through- 
out the  length  of  the  fiber  in  contrast  to  the  medullary  sheath.  In 
the  nerve-fibers  of  the  spinal  cord  and  brain  there  is  no  neurilemma, 
although  the  medullary  sheath  is  present. 

In  the  fresh  nerve-fiber  the  axial  cord  fills  the  space  (axial 
space)  within  the  medullary  sheath,  and  appears  transparent. 
After  treatment  with  many  fixing  fluids  the  neuroplasm  coagulates 
and  shrinks,  no  longer  filling  the  entire  axial  space,  but  appears  in 
the  latter  as  a  wavy  cord  composed  of  an  apparently  homogeneous 


144 


THE    TISSUES. 


mass,  the  fibrillae  of  which  are  no  longer  recognizable.  Such  pic- 
tures, which  formerly  were  supposed  to  represent  the  normal  condi- 
tion of  the  nerve-fibers,  gave  rise  to  the  conception  of  an  axis-cyl- 
inder (vid.  Technic).  That  which  is  known  as  an  axis -cylinder  is 
therefore,  in  reality,  the  changed  contents  of  the  axial  space.  It  may 
be  stated,  however,  that  the  term  axis-cylinder  is  still  much  used, 
since  the  methods  commonly  employed  in  the  investigation  of  the 

nervous  system  do  not 
preserve  the  axial  cord 
in  its  integrity,  but  nearly 
always  result  in  the  for- 
mation of  an  axis-cylin- 
der. Consequently,  al- 
though we  shall  make 
use  of  the  term,  its  limit- 
ations are  to  be  kept  in 
mind. 

Medullated     nerve  - 
fibers  vary  greatly  in  di- 


Ranvier's 
node. 


Fig.  115. — Medullated  nerve-fibers  from  a  rabbit, 
varying  in  thickness  and  showing  internodal  segments 
of  different  lengths.  In  the  fiber  at  the  left  the  neuri- 
lemma  has  become  slightly  separated  from  the  under- 
lying structures  in  the  region  of  the  nucleus  ;  X  I4°- 
Technic  No.  173. 


-  Nucleus. 


Fig.  1 1 6.  —  Remak's  fibers 
(nonmedullated  fibers)  from  the 
pneumogastric  nerve  of  a  rabbit ; 
X  360.  Technic  No.  179. 


ameter,  but  whether  this  points  to  a  corresponding  variation  in 
function  has  not  been  fully  decided.  Fine  fibers  possess  a  diameter 
of  2— 4[Jt,  those  of  medium  size  4—9^,  and  large  fibers  9— 20  p. 
(Kolliker,  93).  A  division  of  medullated  fibers  during  their  course 
through  a  nerve  is  relatively  rare.  The  greater  number  of  fibers  pass 
unbranched  from  their  central  origin  to  the  periphery,  and  only  when 
in  the  neighborhood  of  their  terminal  arborization  do  they  begin  to 
divide.  A  point  of  division  is  always  marked  by  a  node  of  Ranvier. 


THE    NERVOUS    TISSUES.  145 

The  segmental  structure  of  nerve-fibers  would  seem  to  give 
the  impression  that  they  are  formed  by  a  number  of  cells  fused  end 
to  end.  After  what  has  been  said  with  regard  to  ganglion  cells  and 
their  processes,  this  can  be  the  case  only  so  far  as  the  nerve-sheaths 
are  concerned.  According  to  this  theory,  the  formative  cells  of  the 
latter  gather  in  chains  along  the  neu raxes  or  dendrites,  forming  a 
mantle  around  them,  and  in  the  adult  nerve-fibers  taking  the  shape 
of  the  segments  or  internodes  just  described  (His,  87  ;  Boveri,  85). 
The  points  at  which  the  sheath-cells  are  joined  would  then  corre- 
spond to  the  nodes  of  Ranvier.  Other  investigators  have  concluded 
that  the  whole  nerve-fiber  is  developed  from  a  terminal  apposition 
of  ectodermal  cells.  In  this  case  not  only  the  sheaths  of  the  fibers 
but  also  the  corresponding  portions  of  the  nerve  processes  are 
formed  by  them  (KupfTer,  90).  In  both  theories  the  neurilemma 
corresponds  to  the  cell-membrane  ;  in  the  former  the  neurilemma 
nucleus  corresponds  to  that  of  the  sheath-forming  cell,  in  the  latter 
to  that  of  the  formative  cell  of  the  whole  nerve  segment.  It  should 
be  noticed  that,  according  to  the  second  theory,  a  fiber  segment  is 
the  product  of  a  single  cell,  while  according  to  the  first  it  is  evolved 
from  at  least  two  cells  (ganglion  cell  (process)  and  sheath-forming 
cell).  The  former  theory  is  now  very  generally  accepted. 

The  nonmedullated  nerve-fibers,  Remak's  fibers,  possess  no 
medullary  sheath ;  the  axial  cord  shows  nuclei  which  can  be  re- 
garded as  belonging  to  a  thin  neurilemma.  The  majority  of  the 
neuraxes  of  the  neurones  of  the  sympathetic  nervous  system  are  of 
this  structure,  although  small  medullated  nerve-fibers  (the  neuraxes 
of  sympathetic  neurones)  are  found  in  certain  regions. 

All  nerve-fibers,  medullated  as  well  as  nonmedullated,  in  the 
central  and  peripheral  nervous  systems  lose  the  sheaths  here  de- 
scribed before  terminating ;  the  axis-cylinders  (axial  cords)  ending 
without  special  covering  (naked  axis-cylinders).  These  terminal 
branches  are,  in  fixed  and  stained  preparations,  beset  with  small 
thickenings — varicosities — which  vary  greatly  in  size  and  shape. 
Nerve-fibers  presenting  such  appearances  are  spoken  of  as  varicosed 
fibers.  The  varicose  enlargements  may  be  regarded  as  small 
masses  of  neuroplasm  ;  the  fine  uniting  threads,  as  representing  the 
axial  fibrils. 

In  the  peripheral  nervous  system  the  nerve-fibers  are  grouped 
to  form  nerve-trunks.  The  nerve-fibers,  as  has  been  stated  and  as 
will  be  seen  from  the  diagram  (Fig.  117)  on  the  next  page,  are  the 
neuraxes  of  neurones,  the  cell-bodies  of  which  are  situated  in  the 
spinal  cord  or  brain  and  in  the  sympathetic  ganglia,  and  the  den- 
drites of  peripheral  sensory  neurones,  the  cell-bodies  of  which  are 
found  in  the  spinal  and  homologous  cranial  ganglia. 

In  the  nerve-trunks  the  nerve-fibers  are  gathered  into  bundles 
termed  funiculi.  The  nerve-fibers  constituting  such  a  bundle  are 
separated  by  a  small  amount  of  fibre-elastic  tissue,  containing  here 
and  there  connective-tissue  cells,  the  endoneurium.  This  is  continu- 

10 


146 


THE     TISSUES. 


ous  with  a  dense,  lamellated  fibrous  sheath  surrounding  each  funicu- 
lus,  the  perineurium.  Between  the  lamellae  of  this  sheath  are  lymph- 
spaces,  communicating  with  the  lymph-clefts  found  between  the 


Neuraxis  of  peripheral 
sensory  neurone. 


Dendrite  of  per- 
ipheral s  e  n  - 
sory  neurone. 


Spinal  ganglion. 


Anterior  horn  of  gray  matter  of 

spinal  cord. 
Neuraxis  of  peripheral  motor 

neurone. 

—   Sympathetic  ganglion. 


Nerve-trunk. 

Neuraxis  of  sympathetic  neurone. 
Fig.  117. — Diagram  to  show  the  composition  of  a  peripheral  nerve-trunk. 


Epineurium. 


- — Axis-cylinder. 
I  --Neurilemma. 


----- — Endoneurium 


•--Perineuriu 


Fig.  118.— Part  of  a  cross-section  through  a  peripheral  nerve  treated  with  alcohol. 
The  small  circles  represent  the  cross-sections  of  medullated  nerve-fibers  ;  the  axis-cylin- 
ders show  as  points  in  their  centers.  The  nerve  is  separated  by  connective  tissue  into 
large  and  small  bundles — funiculi ;  X  75- 


MOTOR    NERVE-ENDINGS.  147 

nerve-fibers  of  the  funiculi  ;  consequently,  the  lamellae  are  covered 
by  a  layer  of  endothelial  cells.  In  the  larger  funiculi,  septa  of 
fibrous  connective  tissue  pass  from  the  perineurial  sheath  into  the 
funiculi,  dividing  them  into  compartments  varying  in  shape  and  size  ; 
these  are  spoken  of  as  compound  funiculi.  The  funiculi  of  a  nerve- 
trunk  are  bound  together  by  an  investing  sheath  of  loose  fibro-elastic 
tissue,  continuous  with  the  perineurial  sheaths,  which  penetrates 
between  the  funiculi,  and  which  contains  fat-cells,  blood-vessels,  and 
lymph-vessels ;  the  latter  are  in  communication  with  the  lymph- 
spaces  of  the  perineurial  sheaths. 

When  a  nerve-trunk  divides,  the  connective-tissue  sheaths  above 
mentioned  are  continued  on  to  the  branches,  and  this  even  to  the 
smallest  offshoots.  Thus,  single  fibers  even  possess  a  connective- 
tissue  sheath, — Henle's  sheath, — which  consists  of  a  few  connective- 
tissue  fibers  and  of  flattened  cells. 


PERIPHERAL  NERVE  TERMINATIONS. 

According  to  the  character  of  the  peripheral  organs  in  which 
the  telodendria  of  nerve-fibers  (neuraxes  of  type  I  cells  and  dendrites 
of  spinal  ganglion  cells)  occur,  the  nerve-fibers  are  known  as  motor 
and  sensory  nerve-fibers,  the  terminations  as  motor  and  sensory 
nerve-endings. 

Motor  Nerve-endings  (the  Telodendria  of  Nerve-fibers  Ending 
in  Muscle  Tissue). — The  motor  nerve -endings  in  striated,  voluntary 
muscle  tissue  will  first  be  considered.  The  motor  nerve-endings 
in  voluntary  muscle  tissue  are  the  endings  of  neurones  (peripheral 
motor  neurones),  the  cell-bodies  of  which  are  situated  in  the  ventral 
horns  of  the  spinal  cord  and  in  the  medulla.  The  neuraxes  of  these 
cells  leave  the  cerebrospinal  axis  as  medullated  nerve-fibers  (motor 
fibers)  which,  after  branching,  end  in  the  muscle-fibers  in  the  so-called 
motor  endings.  In  figure  119  is  represented,  by  way  of  diagram, 
a  complete  peripheral  motor  neurone.  Each  motor  nerve  -  fiber 
branches  repeatedly  before  terminating,  although  this  branching 
does  not  often  take  place  until  near  the  termination  of  the  nerve- 
fiber.  Kolliker  estimates  that  in  the  sternoradialis  of  the  frog,  each 
motor  fiber  innervates  about  twenty  muscle-fibers  ;  but  whether  this 
number  may  be  regarded  as  the  average  number  of  muscle-fibers 
receiving  their  motor  nerve-supply  from  one  motor  neurone  can  not 
be  stated  with  any  degree  of  certainty  at  the  present  time. 

Each  motor  ending  represents  the  termination  of  one  of  the  ter- 
minal medullated  branches  of  a  motor  nerve-fiber.  The  neuraxis  of 
this  fiber  passes  under  the  sarcolemma  and  terminates  in  a  teloden- 
drion  (end-brush)  in  an  accumulation  of  sarcoplasm,  in  which  are 
found  numerous  muscle  nuclei,  forming  a  more  or  less  distinct  ele- 
vation on  the  side  of  the  muscle-fiber,  Doyere's  elevation.  The 
medullary  sheath  accompanies  the  nerve-fiber  until  it  passes  under 
the  sarcolemma,  when  it  stops  abruptly.  The  neurilemma  of  the 


148 


THE    TISSUES. 


nerve-fiber  becomes  continuous  with  the  sarcolemma  of  the  muscle- 
fiber  at  the  place  where  the  neuraxis  passes  under  the  sarcolemma. 
Henle's  sheath  continues  over  the  motor  ending  as  a  thin  sheath, 
containing  here  and  there  flattened  nuclei,  the  telolemma  nuclei. 

With   the  majority  of  the   reagents  used   to  bring  to  view  the 
motor  endings,  notably  chlorid  of  gold,  the  sarcoplasm,  in  which 


Neuraxis. 


Medullary  sheath. 


Nucleus  of  neurilemma. 


Motor  ending. 


—     Dendrite. 


=^-     Collateral  branch. 
Neurilemma. 


Node  of  Ranvier. 


Internodal  segment. 


Axis-cylinder  of  medullated 

nerve-fiber. 


Muscle-fibers. 


Fig.  119. — Diagram  of  peripheral  motor  neurone. 

the  telodendrion  of  the  nerve-fiber  is  found,  has  a  granular  appear- 
ance, and  is  consequently  differentiated  from  the  remaining  sarco- 
plasm of  the  muscle-fiber.  To  this  the  term  granular  sole  plate  has 
been  applied,  the  nuclei  contained  therein  being  known  as  sole  nuclei, 
the  whole  ending  as  the  motor  end-plate.  If  the  above  interpreta- 


MOTOR    NERVE-ENDINGS.  149 

tion  of  the  structure  of  the  motor  nerve-ending  is  correct,  there 
would  seem  to  be  no  reason  why  the  sarcoplasm  in  which  the  telo- 
dendria  occur  should  be  considered  other  than  the  sarcoplasm  of 
the  muscle-fiber,  the  nuclei  as  muscle-nuclei  ;  the  terms  motor  end- 
plate,  granular  sole  plate,  and  sole  nuclei  would  therefore  seem  un- 
necessary and  misleading.  In  figures  121  to  125  are  shown  motor 
nerve-endings  from  several  vertebrates  as  seen  when  stained  with 
gold  chlorid. 

The  mass  of  sarcoplasm  in  which  the  neuraxes  terminate  as 
above  described  is  about  40  to  60  fj.  long,  40^  broad,  and  6  to  10  p. 
thick  ;  these  dimensions  vary  greatly,  however  ;  they  may  be  greater 
or  less  than  the  averages  here  given. 

In  amphibia  the  motor  nerve-endings  are  not  so  localized  as 
in  the  majority  of  vertebrates,  as  above  described,  but  are  spread 
over  a  relatively  greater  surface  of  the  muscle-fiber,  and  there  is  no 
distinct  accumulation  of  the  sarcoplasm,  and  the  muscle-nuclei  are 


%3 

3»_  "^^ 


Fig.  1 20. — Motor  nerve-ending  in  voluntary  muscle  of  rabbit,  stained  in  methylene- 
blue  (infra  vitatn]  (Huber,  DeWitt,  "Jour.  Comp.  Neurol.,"  vol.  vn)  :  A,  Surface 
view  ;  B,  longitudinal  section  through  motor  ending  ;  C,  cross-section  :  a,  a,  a,  neuraxes 
of  nerve-fibers  ;  s,  s,  s,  sarcolemma  ;  «/,«/,  neurilemma ;  d,  Doyere's  elevation;  mn, 
muscle  nuclei ;  t  n,  telolemma  nucleus. 

relatively  less  numerous.  The  telodendrion  of  the  nerve-fiber  is, 
however,  under  the  sarcolemma,  between  it  and  the  contractile  sub- 
stance of  the  muscle-fiber.  (Fig.  1 26.) 

The  number  of  motor  nerve-endings  in  a  striated,  voluntary 
muscle-fiber  depends  on  its  length,  short  fibers  having,  as  a  rule, 
one  ending,  longer  fibers  two,  or  even  more. 

Heart  muscle-cells  and  nonstriated  muscle-cells  receive  their 
motor  nerve-supply  from  neurones  of  the  sympathetic  nervous  sys- 
tem. The  cell-bodies  of  these  neurones  are  situated  in  sympathetic 
ganglia ;  the  neuraxes,  the  majority  of  which  form  nonmedullated 
nerve-fibers,  branch  repeatedly,  forming  primary  and  secondary 
plexuses  which  surround  the  larger  or  smaller  bundles  of  heart 
muscle-fibers  or  involuntary  muscle-cells.  From  these  plexuses, 
naked,  varicosed  axis-cylinders,  or  small  bundles  of  such,  penetrate 
between  the  muscle-cells,  also  forming  plexuses.  The  fine  fibers 
of  this  terminal  plexus  give  off  from  place  to  place  small,  lateral 


ISO 


THE     TISSUES. 


:     t™==  -_    Nerve. 


Fig.  121. 


Fig.  122. 


Nerve. 


So-called 
granular 
sole. 
—  End-brush. 


So-called 

—  granular 
sole. 

—  End-brush. 


Muscle-          Sarco- 
fiber.  lemma. 


Figs.  123  and  124. 


Fig.  125. 


Figs.  121-125. — Motor  endings  in  striated  voluntary  muscles. 

Fig.  121,  from  Pseudopus  Pallasii ;  X  1 60.  Fig  122,  from  Lacerta  viridis  ;  X  160. 
Figs.  123  and  124,  from  a  guinea-pig;  X  700.  Fig.  125,  from  a  hedge-hog;  X  1200. 
As  a  consequence  of  the  treatment  (T.  182,  I)  the  arborescence  is  shrunken  and  inter- 
rupted in  its  continuity.  In  Figs.  121  and  122  the  end-plate  is  considerably  larger  than 
in  123  and  124.  In  Fig.  121  it  is  in  connection  with  two  nerve-branches.  Fig.  125 
shows  a  section  through  an  end-plate.  The  latter  is  bounded  externally  by  a  sharply  de- 
fined line,  which  can  be  traced  along  the  surface  of  the  muscle-fiber.  This  is  to  be  re- 
garded as  the  sarcolemma. 


SENSORY    NERVE-ENDINGS.  151 

twicrs,  which  end  on  the  muscle-cells.      In  heart  muscle  these  lateral 

o     " 

twigs  may  end  in  one  or  two  small  granules,  or  in  a  small  cluster 
of  such  granules  (Fig.  127)  ;  in  involuntary,  nonstriated  muscle  the 
ending  is  very  simple,  the  small  lateral  twigs  terminating  in  one  or 
two  small  granules.  (Fig.  128.) 

Sensory  Nerve-endings. — The  sensory  nerve-endings  are,  in 
their  essentials,  the  peripheral  telodendria  of  dendrites  of  peripheral 
sensory  neurones.  The  cell-bodies  of  such  neurones,  as  has  been 
stated,  are  found  in  the  spinal  and  homologous  cranial  ganglia. 


Fig.  126. — Motor  nerve-ending  in  striated  voluntary  muscle  of  a  frog  ;  methylene- 
blue  stain  (infra  vifam]  (Huber,  DeWitt)  :  A,  Surface  view  ;  By  cross- section  ;  s,  s, 
sarcolemma  ;  nl,  neurilemma. 


J 


Fig.    127.  — Motor   nerve-ending   on  Fig.    128. — Motor    nerve-ending    on 

heart  muscle-cells  of  cat  ;  methylene-blue  involuntary  nonstriated  muscle-cell  from 
stain  (Huber,  De  Witt).  intestine  of  cat;  methylene-blue  stain 

(Huber,  De  Witt). 

Of  the  two  branches  arising  from  the  single  process  possessed  by 
each  peripheral  sensory  neurone,  the  one  going  to  the  periphery  is 
regarded  as  the  dendrite  and  forms  the  axis-cylinder  of  a  medullated 
nerve-fiber,  such  nerve-fibers  constituting  the  sensory  nerves  of  the 
peripheral  nerve -trunks.  A  peripheral  sensory  neurone  may  there- 
fore be  diagramed  as  in  figure  129.  The  statement  was  made 
above  that  the  essential  portion  of  a  sensory  nerve-ending  is  a  telo- 
dendrion  (end-brush)  or  several  telodendria  of  the  dendrite  of  a 
peripheral  sensory  neurone.  The  character  of  a  sensory  nerve- 


152 


THE    TISSUES. 


ending  depends,  therefore,  on  the  complexity  of  this  end-brush  and 
on  its  relation  to  the  other  tissue  elements  which  take  part  in  the 
formation  of  the  sensory  nerve-endings.  Bearing  this  in  mind,  the 
following  classification  of  such  nerve-endings  can  be  made  : 

I.  Free  Sensory  Nerve-endings. — In  these  the  telodendrion  is  not 


Cell-body.  — 


Process  of  cell. 


Neuraxis,  ends  in  spinal 
cord  or  brain. 


T-shaped  division  of 
Ranvier. 


Dendrite,  a  sensory  nerve- 
fiber  in  nerve-trunk. 


Telodendrion  of 
terminal  branch 
of  dendrite. 


Fig.  129. — Diagram  of  a  peripheral  sensory  neurone. 

inclosed  in  an  investing  capsule  which  forms  a  structural  part  of 
the  ending. 

2.  Encapsulated  Endings. — In  which  the  telodendrion  or  several 
telodendria  are  surrounded  by  an  investing  capsule  which  separates 
them  more  or  less  completely  from  the  surrounding  tissue. 

i.  Free  sensory  nerve-endings  are  found  in  all  epithelial  tis- 
sues and  in  fibrous  connective  tissue  of  certain  regions.  A  sensory 


SENSORY    NERVE-ENDINGS. 


153 


nerve-fiber  terminating  in  such  an  ending  usually  proceeds  without 
branching  to  near  its  place  of  termination,  where,  while  yet  a 
medullated  fiber,  it  branches  and  rebranches  a  number  of  times, 


Fig.  130. — Termination  of  sensory  nerve-fibers  in  the  mucosa  and  epithelium  of  the  ure- 
thra of  cat;  methylene-blue  preparation  (Huber,  "  Jour.  Comp.  Neurol.,"  vol.  x). 


always  at  the  nodes  of  Ranvier,  the  resultant  branches  diverging  at 
various  angles.      If  the  free  sensory  endings  are  in  epithelial  tissue, 


154  THE   TISSUES. 

these  larger  medullated  branches  are  situated  in  the  connective- 
tissue  mucosa  under  the  epithelium.  From  these  larger  medullated 
branches,  are  given  off  smaller  ones,  also  medullated,  which  may 
divide  further,  and  which  pass  up  toward  the  epithelium,  and  near  its 
under  surface  divide  into  nonmedullated  branches.  Nonmedullated 
branches  are  also  given  off  from  the  medullated  ones  as  they 
approach  the  epithelium,  leaving  the  parent  fibers  at  the  nodes  of 
Ranvier.  Many  of  the  nonmedullated  branches  thus  formed,  after 
coursing  a  variable  distance  under  the  epithelium,  enter  it  and  break 
up  into  numerous  very  small  branches,  which,  after  repeated  divi- 
sion, terminate  between  the  epithelial  cells  in  small  nodules  or 
discs  of  variable  size  and  configuration.  The  small  branches  result- 
ing from  a  division  of  one  of  the  larger  nonmedullated  branches 
constitute  one  of  the  terminal  telodendria  or  end-branches  of  the 
dendrites  of  peripheral  sensory  neurones  terminating  in  free  sensory 
nerve-endings.  In  fibrous  connective  tissue  the  same  general 
arrangement  of  the  branches  prevails.  In  figure  130  is  shown  the 
peripheral  distribution  of  the  dendrite  of  a  peripheral  sensory 
neurone  terminating  in  a  free  sensory  nerve-ending. 

2.   Encapsulated   Sensory  Nerve=endings. — These  nerve-end- 
ings maybe  divided  into  two  quite  distinct  groups, — such  as  have  a 

relatively  thin  fibrous-tissue  capsule, 
containing  mainly  telodendria  of  the 
nerve  or  nerves  terminating  therein, 
and  such  as  have  a  distinctly  lamel- 
lated,  fibrous  tissue  capsule,  usually 
investing,  besides  the  nerve-termi- 
nation, other  tissue  elements.  To 
the  former  group  belong  three  types 
of  sensory  nerve  -  endings,  which, 
owing  to  their  similarity  of  struc- 
„.  ,  ^  ture,  may  be  described  together. 

Fig.    131.— End-bulb  of   Krause       ~,,     •  ,  .     .,         -  T° 

from  conjunctiva  of  man  ;  methylene-  These  are  the  end-bulbs  of  Krause, 
blue  stain  (Dogiel,  "Arch.  f.  mik.  Meissner's  tactile  corpuscles,  and 

Anat.,"  vol.  xxxvn).  the  genital  corpuscles.      They  have 

all   been   investigated    recently  by 

Dogiel,  and  the  account  here  given  follows  closely  his  description. 
End-bulbs  of  Krause. — Under  this  designation  there  are  described 
a  variety  of  endings  which  vary  slightly  in  size  and  shape.  They 
are  found  in  the  conjunctiva  and  edge  of  the  cornea,  in  the  lips  and 
lining  of  the  oral  cavity,  in  the  glans  penis  and  clitoris,  and  prob- 
ably also  in  other  parts  of  the  dermis.  In  form  they  are  round, 
oval,  or  pear-shaped.  Their  size  varies  from  0.02  to  0.03  mm. 
long  and  from  0.015  to  0.025  mm.  broad  for  the  smaller  ones, 
and  from  0.045  to  ai°  mm-  l°ng  and  from  0.02  to  0.08  mm. 
broad  for  the  larger  ones.  They  have  a  relatively  thin  capsule 
in  which  nuclei  are  quite  numerous.  One,  two,  or  three  medul- 
lated nerves  go  to  each  end-bulb.  These  may  lose  their  medul- 


SENSORY    NERVE-ENDINGS. 


155 


lary  sheath  at  the  capsule  or  at  a  variable  distance  from  it.  The 
naked  axis-cylinders,  soon  after  entering  the  capsule,  divide  into  two, 
three,  or  four  branches,  which  form  several  circular  or  spiral  turns 
in  the  same  or  in  opposite  directions.  These  fibers  then  divide  into 
varicose  branches,  which  undergo  further  division,  the  resulting 
branches  interlacing  to  form  a  bundle  of  variously  tangled  fibers 
which  may  be  loosely  or  tightly  woven. 

Between  the  nerve-fibers  and  their  branches,  within  the  capsule, 
there    is  found   a    semifluid    sub- 
stance, which  is  granular  in  fixed 
preparations. 

Mcissner 's  Corpuscles. — These 
corpuscles  are  found  in  man  in 
the  subepidermal  connective  tissue 
of  the  hand  and  foot  and  outer 
surface  of  the  forearm,  in  the  nip- 
ple, border  of  the  eyelids,  lips, 
glans  penis  and  clitoris.  They  are 
most  numerous  in  the  palmar  sur- 
face of  the  distal  phalanx  of  the 
fingers.  They  are  oval  in  shape, 
sometimes  somewhat  irregular, 
and  vary  in  size,  being  from  45  ft 
to  50  /JL  broad  and  from  1 10  p  to 
1 80  p.  long.  They  possess  a  thin 
connective-tissue  capsule,  in  which 
are  found  round  or  oval  nuclei, 
some  of  which  have  an  oblique 
position  to  the  axis  of  the  corpus- 
cle. One  medullated  nerve  ends 
in  the  smaller  corpuscles,  two  or  j 
three  or  even  more  in  the  larger 
ones.  After  piercing  the  capsule, 
the  medullated  nerves  lose  their 

medullary  sheaths,  the  naked  axis-cylinders  making  a  variable 
number  of  circular  or  spiral  turns,  some  of  which  are  parallel,  others 
crossing  at  various  angles.  These  larger  branches  are  all  beset 
with  large,  spindle-shaped,  round,  or  pear-shaped  varicosities.  The 
larger  branches,  after  making  the  windings  mentioned,  break  up' 
into  many  varicose  branches,  which  interlace  and  form  a  most  com- 
plex network.  One  usually  finds  one  or  several  larger  naked  axis- 
cylinders,  which  pass  up  through  the  axis  of  the  spiral  of  fibers 
thus  formed  ;  these  give  ofif  branches  which  contribute  to  the  spiral 
formation. 

Genital  Corpuscles. — These  corpuscles  are  found  in  the  deeper 
part  of  the  mucosa  of  the  glans  penis  and  the  prepuce  of  the 
male  and  the  clitoris  and  neighboring  structures  of  the  female. 
Their  shape  varies ;  they  may  be  round,  oval,  egg-  or  pear- 


Fig.  132. — Meissner's  tactile  corpus- 
methylene-blue  stain  (Dogiel,  "  In- 

ternat.   Monatsschr.  f.  Anat.  u.  Phys.," 

vol.  ix). 


1 56 


THE    TISSUES. 


shaped,  or  even  slightly  tabulated.  Their  size  varies  from  0.04 
to  o.  10  mm.  in  breadth  and  from  0.06  to  0.40  mm.  in  length.  They 
are  surrounded  by  a  relatively  thick  fibrous  capsule,  consisting 
of  from  three  to  eight  quite  distinct  lamellae,  between  which  irregu- 
lar flattened  cells  with  round  or  oval  nuclei  are  found.  Within 
this  capsule,  there  is  found  a  core,  which  seems  to  consist  of  a  semi- 
fluid substance,  slightly  granular  in  fixed  preparations,  the  nature 
of  which  is  not  fully  known.  The  number  of  sensory  nerves  going 
to  each  corpuscle  varies  from  one  to  two  for  the  smaller  ones,  and 
from  eight  to  ten  for  the  larger  corpuscles.  The  medullated  nerves, 
after  entering  the  corpuscle,  divide  dichotomously,  the  resultant 
branches  assuming  a  circular  or  spiral  course,  and  interlacing  in 
various  ways,  within  the  capsule.  After  a  few  turns,  the  medullated 

branches  lose  their  medullary 
sheaths  and  undergo  further  di- 
vision, often  dividing  repeatedly. 
The  nonmedullated  nerves  re- 
sulting from  these  divisions,  the 
majority  of  which  are  varicose, 
form  a  most  complicated  net- 
work, the  whole  nerve  network 
presenting  a  structure  which  re- 
sembles a  tangle  of  fine  threads. 
In  the  meshes  of  this  network  is 
found  the  semifluid  substance 
of  the  core.  Now  and  then 
some  of  the  larger  fibers  of  the 
network  leave  the  corpuscle 
and  terminate  in  neighboring 
corpuscles,  or  pass  to  the  epi- 
thelium, where  they  end  be- 
tween the  cells. 

These  three  sensory  nerve- 
endings — end-bulbs  of  Krause, 
Meissner's  tactile  corpuscles,  genital  corpuscles — are,  as  Dogiel  has 
stated,  very  similar  in  structure.  Each  has  a  thin  connective -tissue 
capsule,  surrounding  a  core,  consisting  of  a  semifluid  substance, 
concerning  which  our  knowledge  is  as  yet  imperfect.  One  or  sev- 
eral medullated  nerves  go  to  each  corpuscle,  which,  after  losing 
their  medullary  sheaths,  divide  and  subdivide  into  numerous  fine 
varicose  branches,  which  are  variously  interwoven,  forming  a  more 
or  less  dense  plexus  of  interlacing  and,  according  to  <  Dogiel,  anas- 
tomosing fibers.  The  chief  differences  are  those  of  form  and  size, 
and  of  position  with  reference  to  the  epithelium.  Of  the  three  forms 
of  endings,  the  genital  corpuscle  is  the  largest,  and  occupies  the  deep- 
est position  in  the  subepithelial  connective  tissue  ;  Meissner's  cor- 
puscle is  intermediate  in  size,  and  is  found  immediately  under  the 
epithelium  ;  while  the  end-bulbs  of  Krause  are  the  smallest  of  these 


Fig.  133. — Genital  corpuscle  from  the 
glans  penis  of  man  ;  methylene-blue  stain 
(Dogiel,  "Arch.  f.  mik.  Anat.,"  vol.  XLl). 


SENSORY    NERVE-ENDINGS.  157 

three  forms  of  sensory  endings  and  may  be  found  in  the  papillae  or 
in  the  deeper  connective  tissue. 

A  somewhat  smaller  nerve-ending  of  long,  oval,  or  cylindric 
form,  known  as  the  cylindric  end-bulb  of  Krause,  is  found  in  various 
parts  of  the  skin  and  oral  mucous  membrane,  in  striated  muscle 
and  in  tendinous  tissue.  These  corpuscles  consist  of  a  thin  nucle- 
ated capsule,  investing  a  semifluid  core.  The  nerve-fiber,  after 
losing  its  medullary  sheath  and  fibrous  sheath  (the  latter  becomes 
continuous  with  the  capsule),  passes  through  the  core,  generally 
without  branching,  as  a  naked  axis-cylinder,  terminating  at  its  end, 
usually  in  a  small  bulb.  (Fig.  134.) 

The  majority  of  the  sensory  nerve-endings  with  well-developed 
lamellated  capsules  are  relatively  large  structures.     We  shall  con- 
sider especially  the  Vater-Pacin- 
ian    corpuscles,    the    neuromus- 
cular  end-organs,  and  the  neuro- 
tendinous  end-organs. 

Vater-Paciniaii  Corpuscles. — 
These  corpuscles  are  of  oval 
shape  and  vary  much  in  size,  the 
largest  being  about  o.  10  of  an 
inch  long  and  0.04  of  an  inch  Fig.  i34._  Cylindric  end-bulb  of 

broad        The    greater  portion    of        Krause   from   intermuscular  fibrous   tissue 
the    Corpuscle    is    made    up    of  a       septum  of  cat;  methylene-blue  stain. 

series  of  concentric  lamellae,  vary- 
ing in  number  from  twenty  to  sixty.  These  lamellae  are  made  up  of 
white  fibrous  tissue  fibers,  rather  loosely  woven,  between  which  is 
found  a  small  amount  of  lymph,  containing  usually  a  few  leucocytes. 
The  lamellae  are  covered  on  both  surfaces  by  a  layer  of  endothelial 
cells  (Schwalbe).  Between  two  consecutive  lamellae  there  is  found  an 
interlamellar  space,  also  containing  lymph.  The  axis  of  the  cor- 
puscle is  occupied  by  a  core,  consisting  of  a  semifluid,  granular 
substance,  in  the  periphery  of  which  oval  nuclei  are  said  to  be 
found.  Usually  one  large  medullated  nerve-fiber  goes  to  each  cor- 
puscle. The  fibrous  tissue  sheath  of  this  nerve-fiber  becomes  con- 
tinuous with  the  outer  lamellae  of  the  capsule.  The  medullary 
sheath  accompanies  the  axis-cylinder  through  the  concentric  lamel- 
lae until  the  core  is  reached,  where  it  disappears.  The  naked  axis- 
cylinder  usually  passes  through  the  core  to  its  distal  end,  where  it 
divides  into  three,  four,  or  five  branches  which  terminate  in  large, 
irregular  end-discs.  The  axis-cylinder  may,  however,  divide  soon 
after  it  enters  the  core  into  two  or  three  or  even  four  branches, 
these  passing  to  the  distal  end  of  the  core  before  terminating  in  the 
end-discs  above  mentioned.  Both  Retzius  and  Sala  state  that  the 
naked  axis-cylinders,  after  entering  the  core,  give  off  numerous  short 
side  branches,  terminating  in  small  knobs,  which  remind  these  ob- 
servers of  the  fine  side  branches  or  thorns  seen  on  the  dendrites  of 
Purkinje's  cells  and  of  the  pyramidal  cells  of  the  cortex,  when  stained 


158 


THE     TISSUES. 


after  the  Golgi  method.  In  company  with  the  large  nerve-fibers  here 
mentioned,  Sala  has  described  other  nerve-fibers,  quite  independent 
of  them  and  much  finer,  which  after  entering  the  corpuscle  divide 
repeatedly,  the  resulting  fibers  forming  a  plexus  around  the  central 
fiber.  A  small  arteriole  enters  the  corpuscle  with  the  nerve-fiber, 
dividing  into  capillary  branches  found  between  the  lamellae  of 
the  capsule. 

The  Vater-Pacinian  corpuscles  have  a  wide  distribution.  They 
are  numerous  in  the  deeper  parts  of  the  dermis  of  the  hand  and 
foot,  and  also  near  the  joints,  especially  on  the  flexor  side.  They 
have  been  found  in  the  periosteum  of  certain  bones  and  in  tendons 
and  intermuscular  septa,  and  even  in  muscles.  They  are  further 
found  in  the  epineurial  sheaths  of  certain  nerve-trunks  and  near 


Fig.  135. — Pacinian  corpuscles  from  mesorectum  of  kitten  :  A,  Showing  the  fine 
branches  on  central  nerve-fiber ;  B,  the  network  of  fine  nerve-fibers  about  the  central 
fiber;  methylene-blue  preparation  (Sala,  "Anat.  Anzeiger,"  vol  xvi). 

large  vessels.  They  are  numerous  in  the  peritoneum  and  mesentery, 
pleura  and  pericardium.  In  the  mesentery  of  the  cat,  where  these 
nerve-endings  are  large  and  numerous,  they  are  readily  seen  with  the 
unaided  eye  as  small,  pearly  bodies. 

In  the  bill  and  tongue  of  water  birds,  especially  of  the  duck,  are 
found  nerve-endings,  known  as  the  corpuscles  of  Herbst,  which  re- 
semble the  Vater-Pacinian  corpuscles  ;  they  differ  from  the  latter  in 
having  cubic  cells  in  the  core,  (Fig.  136.) 

Neuromuscular  Nerve  End-organs. — These  nerve  end-organs 
consist  of  a  small  bundle  of  muscle-fibers,  surrounded  by  an  invest- 


SENSORY    NERVE-ENDINGS. 


159 


ing  capsule,  within  which  one  or  several  sensory  nerves  terminate. 
They  are  spindle-shaped  structures  varying  in  length  from  0.75  to  4 
mm.,  and  in  breadth,  where  widest,  from  80  to  200  /JL  (Sherrington, 
94).  In  them  there  is  recognized  a  proximal  polar  region,  an 
equatorial  region,  and  a  distal  polar  region.  The  muscle-fibers  of 
this  nerve-ending,  known  as  the  intrafusal  fiber S>  which  may  vary  in 
number  from  3  or  4  to  20  or  even  more,  are  much  smaller  than  the 
ordinary  voluntary  muscle-fibers  and  differ  from  them  structur- 
ally, and  result  from  a  division  of  one  or  several  muscle-fibers  of 
the  red  variety.  In  the  proximal  polar  region  the  intrafusal  fibers 
present  an  appearance  which  is  similar  to  that  of  voluntary  muscle- 
fibers  of  the  red  variety  ;  in  the  equatorial  region  they  possess  rela- 


-  Nucleus  of  lamellae. 


End-cell  of  core. 
Lamellae. 

Axis-cylinder  in  core. 
Cubic  cells  of  core. 

Termination  of  medul- 
lary sheath. 


Axis-cylinder  of 
nerve-fiber. 


Medullary  sheath  of 

nerve-fiber. 
Neurilemma  and  sheath 

of  Henle. 


Fig.  136. — Corpuscle  of  Herbst  from  bill  of  duck  ;   X  6°°'     Technic  No.  296. 

tively  few  muscle-fibrils  and  are  rich  in  sarcoplasm  and  the  muscle- 
nuclei  are  numerous  ;  the  striation  is  here  indistinct.  In  the  distal 
polar  region  the  intrafusal  fibers  are  again  more  distinctly  striated 
and,  a  short  distance  beyond  the  end-organ,  become  greatly  reduced 
in  size,  and  terminate  as  very  small  fibers,  still  showing,  however,  a 
cross-striation.  In  figure  137  is  shown  a  single  intrafusal  muscle- 
fiber.  Owing  to  the  length  of  such  a  fiber  it  was  necessary  to  rep- 
resent it  in  several  segments. 

The  intrafusal  muscle-fibers  are  surrounded  by  a  capsule  con- 
sisting of  from  four  to  eight  concentric  layers  of  white  fibrous  tissue. 
At  the  proximal  end  this  capsule  is  continuous  with  the  connective 


160  THE     TISSUES. 

tissue  found  between  the  muscle-fibers — endo-  and  perimysium.  It 
attains  its  greatest  diameter  in  the  equatorial  region  of  the  nerve 
end-organ,  and  becomes  narrower  again  at  its  distal  end,  where  it 
may  end  in  tendon  or  become  continuous  with  the  connective  tissue 


Fig.  137. — Intrafusal  muscle-fiber  from  neuromuscular  nerve  end-organ  of  rabbit : 
A,  From  proximal  polar  region  ;  B,  equatorial  region  ;   C,  distal  polar  region. 

of  the  muscle.  Immediately  surrounding  the  intrafusal  fibers  is  found 
another  connective -tissue  sheath  known  as  the  axial  sheath,  and 
between  this  and  the  capsule  there  is  found  a  lymph-space  bridged 
over  by  trabeculae  of  fibrous  tissue,  to  which  the  name  periaxial 
lymph-space  has  been  given.  (Fig.  138.) 

By  degenerating  the  motor  nerves  going  to  a  muscle,  Sherrington 


, 


Hpi 

'    v 

Fig.  138. — Cross-section  of  a  neuromuscular  nerve  end-organ  from  interosseous  (foot) 
muscle  of  man  ;  fixed  in  formalin  and  stained  in  hematoxylin  and  eosin. 

determined  that  the  nerve-fibers  ending  in  the  neuromuscular  nerve 
end-organs  were  sensory  in  character.  The  manner  of  termination  in 
these  end-organs  of  the  nerve-fibers  ending  therein  has  been  studied 
by  Kerschner,  Kolliker,  Ruffini,  Huber  and  DeWitt,  and  others. 


SENSORY    NERVE-ENDINGS. 


161 


One  or  several  (three  or  four)  large  medullated  nerves,  surrounded 
by  a    sheath   of    Henle,    terminate    in  each    neuromuscular  end- 


Fig.  139. — Neuromuscular  nerve  end-organ  from  the  intrinsic  plantar  muscles  of 
dog  ;  from  teased  preparation  of  tissue  stained  in  methylene-blue.  The  figure  shows  the 
intrafusal  muscle-fibers,  the  nerve-fibers  and  their  terminations  ;  the  capsule  and  the  sheath 
of  Henle  are  not  shown  (Huber  and  DeWitt,  "Jour.  Comp.  Neurol.,"  vol.  vn). 

organ.     As  these  nerves   enter  the  capsule,  the  sheath   of  Henle 
blends   with  the  capsule.     The  medullated  nerve-fibers   now  and 
ii 


162 


THE     TISSUES. 


then  divide  before  reaching  the  nerve  end-organs,  and  divide  several 
times  as  they  pass  through  the  capsule,  periaxial  space,  and  axial 
sheath.  Within  the  axial  sheath,  the  medullary  sheath  is  lost,  and 

the  naked  axis-cylinders  terminate  in 
one  or  several  ribbon  -  like  branches 
which  are  wound  circularly  or  spirally 
about  the  intrafusal  fibers  (annulospiral 
ending)  or  they  may  terminate  in  a 
number  of  larger  branches  which  again 
divide,  these  ending  in  irregular,  round, 
oval,  or  pear-shaped  discs  (flower-like 
endings),  which  are  also  on  the  intra- 
fusal fibers.  These  flower-like  endings 
are  usually  at  the  ends  of  the  annulo- 
spiral fibers.  In  the  smaller  end- 
organs  only  one  area  of  nerve-termi- 
nation has  been  observed ;  in  the 
larger,  two,  three,  or  even  four  such 
areas  may  be  found. 

Neuromuscular  nerve  end-organs 
are  found  in  nearly  all  skeletal  muscles 
(not  in  the  extrinsic  eye  muscles  nor 
in  the  intrinsic  muscles  of  the  tongue), 
but  they  are  especially  numerous  in 
the  small  muscles  of  the  hand  and  foot. 
T,hey  are  found  in  amphibia,  reptilia, 
birds,  and  mammalia,  presenting  the 
same  general  structure,  although  the 
ultimate  termination  of  the  nerve-fibers 
varies  somewhat  in  the  different  classes 
of  vertebrates. 

Neurotendinous  Nerve  End -organ 
(Golgi  Tendon  Spindle).  —  In  1880 
Golgi  drew  attention  to  a  new  nerve 
end-organ  found  in  tendon,  describing 
quite  fully  its  general  structure  and 
less  fully  the  nerve  termination  found 
therein.  These  nerve  end-organs  are 
spindle-shaped  structures,  which  in 
man  vary  in  length  from  1.28  mm.  to 
1.42  mm.,  and  in  breadth  from  0.17 
mm.  to  0.25  mm.  (Kolliker).  Ciaccio 
mentions  a  neurotendinous  nerve  end- 
organ  found  in  a  woman,  which  was  2 
Fig.  140.  -  Neurotendinous  °r  3  mm.  long.  A  capsule  consisting  of 

nerve  end-organ  from  rabbit;  teased  from  2  to  6  fibrous  tissue  lamellae,  and 
preparation  of  tissue  s.tained  in  Ktv^o/^ef  of  fV.^  ^/-mofrM-ial  t~»oH-  ^f  fVi^ 

methylene-blue(HuberandDeWitt,  broadest  at  the  equatorial  part  of  the 
"Jour.  Comp.  Neurol.,"  vol.  x).  end-organ,  surrounds  a  number  of  in- 


SENSORY    NERVE-ENDINGS.  163 

trafusal  tendon  fasciculi.  The  capsule  is  continuous  at  the  prox- 
imal and  distal  ends  of  the  end-organ  with  the  internal  periten- 
dineum  of  the  tendon  in  which  it  is  found.  The  number  of  the 
intrafusal  tendon  fasciculi  varies  from  eight  to  fifteen  or  even  more. 
They  are  smaller  than  the  ordinary  tendon  fasciculi,  from  which 
they  originate  by  division,  and  structurally  resemble  embryonic 
tendon,  in  that  they  stain  more  deeply  and  present  many  more 
nuclei  than  fully  developed  tendon.  The  intrafusal  tendon  fasciculi 
are  surrounded  by  an  axial  sheath  of  fibrous  tissue,  between  which 
and  the  capsule  there  is  found  a  periaxial  lymph-space. 


mi  ss 


Fig.  141. — Cross-section  of  neurotendinous  nerve  end-organ  of  rabbit;  from  tissue 
stained  in  methylene-blue  :  m,  Muscle-fibers  ;  t,  tendon  ;  c,  capsule  of  neurotendinous 
end-organ  ;  /;/«,  medullated  nerve-fiber  (Huber  and  DeWitt,  "Jour,  of  Comp.  Neurol.," 
vol.  X). 

The  termination  of  the  nerve-fibers  ending  in  these  end-organs 
has  been  studied  by  Golgi,  Cattaneo,  Kerschner,  Kolliker,  Pansini, 
Ciaccio,  Huber  and  DeWitt.  One,  two,  or  three  large  medullated 
nerve-fibers,  surrounded  by  a  sheath  of  Henle,  end  in  each  end- 
organ  ;  as  they  pass  through  the  capsule,  the  sheath  of  Henle 
blends  with  the  capsule.  The  medullated  nerve-fibers  before  enter- 
ing the  capsule  usually  branch  several  times,  branching  further 
within  the  capsule  and  axial  sheath.  Before  the  resultant  branches 
terminate  on  the  intrafusal  tendon  fasciculi,  the  medullary  sheath  is 


164  THE     TISSUES. 

lost,  the  naked  axis-cylinder  further  dividing  into  two,  three,  or  four 
branches,  each  of  which  runs  along  on  the  intrafusal  fasciculi,  giving 
off  numerous  short,  irregular  side  branches,  which  partly  enclasp 
the  tendon  fasciculi  and  end  in  irregular  end-discs.  Some  of  the  ter- 
minal branches  pass  between  the  smaller  fibrous  tissue  bundles  of 
the  fasciculi,  ending  between  them. 

In  these  end-organs,  the  larger  nerve-branches  are  found  near 
the  center  of  the  bundle  of  intrafusal  tendon  fasciculi,  the  terminal 
branches  and  the  end-discs  nearer  their  periphery.  The  neuroten- 
dinous  nerve  end-organs  are  widely  distributed,  being  found  in  all 
tendons  although  not  equally  numerous  in  all.  Like  the  neuromus- 
cular  nerve  end-organs,  they  are  especially  numerous  in  the  small 
tendons  of  the  hand  and  foot.  Sensory  nerve  end-organs,  which 
resemble  in  structure  the  neurotendinous  end-organs  here  described, 
though  somewhat  smaller  than  these,  have  been  found  in  the  tendons 
of  the  extrinsic  eye-muscles. 

In  this  brief  account  of  the  mode  of  ending  of  the  telodendria  of 
the  dendrites  of  peripheral  sensory  neurones  (sensory  nerve-fibers) 
it  has  not  been  possible  to  discuss  any  but  the  more  typical  varie- 
ties of  sensory  nerve-endings.  Other  nerve -endings  will  be  consid- 
ered in  connection  with  the  several  organs  to  be  treated  later.  For 
a  fuller  discussion  of  this  subject,  the  reader  is  referred  to  special 
works  and  monographs. 

TECHNIC 

173.  Fresh  medullated  nerve-fibers,  when  teased  in  an  indifferent 
fluid  (vid.  T.  13),  show  the  peculiar  luster  of  the  medullary  sheath,  and 
also  the  nodes  of  Ranvier,  the  neurilemma  with  its  nuclei,  and  the  seg- 
ments of  Lantermann.     At  the  cut  ends  of  the  fibers,  the  typical  coagula- 
tion of  their  medullary  portions  is  seen  in  the  form  of  drops  of  myelin. 
All  these  structures  can  also  be  seen  after  using  i  °/0  osmic  acid.    A  nerve 
(not  too  thick)  is  placed   in  a  i  °/c   aqueous  osmic  acid   solution,  then 
washed  for  a  few  hours  in  distilled  water,  and   finally  carried  over  into 
absolute  alcohol.     After  dehydration,  small  pieces  are  cleared  with  oil  of 
cloves  and  the  fibers  teased  apart  upon  a  slide.     The  medullary  sheath  is 
stained  black  and   hides   the  axial  space,  the  nodes  are  clear,  the  neu- 
rilemma is  sometimes  seen  as  a  light  membrane,  and  the  nuclei  of  the 
fibers  are  of  a  lenticular  shape,  and  stained  brown. 

174.  The  nodes  of  Ranvier  may  also  be  demonstrated  by  means  of 
silver  nitrate  solution.      Fresh  nerve-fibers  are  either  teased  in  distilled 
water  to  which  a  trace  of  i%  silver  nitrate  solution  has  been  added  (the 
nodes  of  Ranvier  appear  after  a  short  time  as  small  crosses),  or  whole 
nerves  are   placed   for  twenty-four  hours  in  a  0.5%   aqueous  solution 
of  silver   nitrate,   washed    for  a    short    time  with  water,    hardened    in 
alcohol,  after  which  they  are  imbedded  in  paraffin  and  cut  longitudinally. 
Exposure  to  light  will  soon  bring  out  the   "  crosses  of  Ranvier"  at  the 
nodes.     The  appearance   of  these   crosses  is  due  to   the   fact  that   the 
silver  nitrate  solution  first  penetrates  at  the  nodes  of  Ranvier,  and  then 
passes  by   capillary  attraction  along  the  axial   cord  for  some  distance. 
After  the  reduction  of  the  silver,  the  cruciform   figures  appear  colored 


THE    NERVOUS    TISSUES. 


i65 


black.  Occasionally,  a  peculiar  transverse  striation  is  seen  in  the  longi- 
tudinal portions  of  the  crosses.  These  are  known  as  Frommann's  lines. 
Their  origin  and  significance  have  not  as  yet  been  satisfactorily  ex- 
plained. 

175.  To  demonstrate  the  fibrils  of  the  axial  cord  a  piece  of  a  small 
nerve  is  stretched  on  a  match  or  toothpick  and  fixed  for  four  hours  in  a 
0.5%  osmic  acid  solution,  after  which  it  is  washed  in  water  for  the  same 
length  of  time  and  immersed  in  90  °/0  alcohol  for  twenty-four  hours.  The 
preparation  is  now  stained  for  another  twenty-four  hours  in  a  saturated 
aqueous  solution  of  fuchsin  S  and 
then  placed  for  three  days  in  abso- 
lute alcohol.  Finally,  the  nerve  is 
passed  as  rapidly  as  possible  through 
toluol,  toluol- paraffin,  and  then  im- 
bedded in  paraffin.  The  proper 
orientation  of  the  specimen  is  of  the 
greatest  importance,  as  is  also  the 
cutting  of  thin  sections.  In  a  lon- 
gitudinal section  red  fibrils  of  almost 
uniform  thickness  and  evenly  dis- 
tributed throughout  the  axial  space  Axis-cyiin- 
are  seen  lying  in  the  colorless  neuro- 


Medullary 
sheath.     


Fig.  142. — Ranvier's  crosses  from  sci- 
atic nerve  of  rabbit ;  X  * 2O-  Technic  No. 
174.  Frommann's  lines  can  be  seen  in  a 
few  fibers. 


Fig.  143. — Medullated  nerve-fiber  from 
sciatic  nerve  of  frog.  In  two  places  the 
medullary  sheath  has  been  pulled  away 
by  teasing,  showing  the  '*  naked  axis-cylin- 
der" ;  X212-  Technic  No.  176. 


plasm,  and  parallel  to  the  long  axis  of  the  nerve-fiber.  In  cross-section 
the  axial  fibrils  appear  as  evenly  distributed  dots.  Attention  must  be 
called  to  the  fact  that  the  fibrils  are  not  equally  well  stained  in  all  cases 
(Kupffer,  83,  II ;  compare  also  Jacobi  and  Joseph). 

176.  When  the  fiber  is  less  carefully  treated,  the  fibrils  fuse  with  the 
neuroplasm  to  form  the  "axis-cylinder"  of  authors.  As  the  appearance 
of  the  latter  is  due  to  a  shrinkage  of  the  contents  of  the  axial  space,  it  is 
easy  to  understand  that  one  reagent  may  have  a  greater  effect  in  this  re- 
spect than  another.  The  thinnest  axis-cylinders  are  produced  by  chromic 
acid  and  its  salts,  while  thicker  ones  are  seen  in  nerve-fibers  fixed  in 
alcohol.  These  variations  are  best  seen  in  cross-sections,  in  which  the 


1 66 


THE    TISSUES. 


.  Dendrite. 


axis-cylinders  sometimes  appear  as  round  dots  and  again  as  stellate  figures. 
The  latter  are  due  to  pressure  on  the  shrinking  axial  cord  by  the  unevenly 
coagulated  medullary  sheath. 

As  the  medullary  sheath  in  such  preparations  crumbles  away  in  many 
places,  large  areas  of  the  axis-cylinder  may  often  be  isolated  by  teasing 
(Fig.  143). 

177.  If  freshly  teased  fibers  be  treated  with  glacial  acetic  acid,  the 
axis-cylinders  swell  up  and  issue  from  the  ends  of  the  fibers  in  irregular 
masses  showing  fine  longitudinal  striation  (Kolliker,  93).     The  structures 
of  the  axial  space  dissolve  in  i^  hydrochloric  acid,  as  well  as  in  a  10% 
solution  of  sodium  chlorid  (Halliburton). 

178.  For  the  isolation  of  ganglion  cells,  33%  alcohol,  o.i  to  0.5% 
chromic  acid,  or  i^   solution  of  potassium  bichromate   may  be  used. 

Small  pieces  of  the  spinal 
cord  and  brain  containing 
ganglion  cells  are  treated 
with  a  small  quantity  of 
one  of  the  above  solutions 
for  one  or  two  weeks.  After 
this  interval  the  prepara- 
tions may  be  teased  and 
the  isolated  ganglion  cells 
stained  on  a  slide  and 
mounted  in  glycerin.  They 
may  even  be  fixed  in  situ 
by  injecting  a  i  °/0  solution 
of  osmic  acid  or  33%  al- 
cohol into  the  areas  of 
the  brain  or  spinal  cord 
containing  ganglion  cells. 
The  region  thus  treated  is 
then  cut  out  and  teased. 

In  preparations  fixed 
in  alcohol  and  stained  with 
thionin,  or  in  those  treated 
with  corrosive  sublimate 
and  subsequently  stained 
with  hematoxylin,  chro- 
matophile  bodies  are  seen 
in  the  ganglion  cells. 

179.  The    nonmedullated    or  "  Remak's    fibers"    are    obtained  by 
teasing  a  sympathetic  nerve,  or,  better,  a  piece  of  the  vagus  previously 
treated  with  osmic  acid.      Between  the  blackened  medullated  fibers  of  the 
pneumogastric  are  seen  numerous  unstained  fibers  of  Remak. 

The  fibers  of  the  olfactory  nerves  are  stained  brown  by  osmic  acid. 

180.  Short  muscles  (ocular  muscles  or  intercostal  muscles)  are  em- 
ployed in  demonstrating  the  motor  nerve-endings  in  muscles,  the  fresh 
specimen  being  treated  with  i  %  acetic  acid. 

181.  Furthermore,  the  gold  methods  for  the  demonstration  of  the 
nerve-fibers  in  the  cornea,   first  discovered  by  Cohnheim  (67,  II)  and 
still  used  to-day,  may  be  employed  :    Small  pieces  of  muscle  are  placed 
in  a  i  %   solution  of  gold  chlorid  acidulated  by  a  trace  of  acetic  acid. 


„   v- Nucleus. 
x    'Nucleolus. 
'  Cell-body. 


Neuraxis. 


Fig.  144. — A  ganglion  cell  from  anterior  horn 
of  the  spinal  cord  of  calf ;  teased  preparation  ; 
X  140-  Technic  No.  178.  By  this  method  only  the 
coarsest  ramifications  of  the  dendrites  are  preserved  ; 
the  rest  are  torn  off. 


THE    NERVOUS    TISSUES.  l6/ 

In  this  they  become  yellow  (in  from  a  few  minutes  to  half  an  hour).  They 
are  then  rinsed  in  distilled  water,  placed  in  water  slightly  acidulated  with 
acetic  acid,  and  kept  in  the  dark.  As  a  rule,  the  pieces  will  change  in 
color,  becoming  yellowish-gray,  grayish-violet,  and  finally  red,  from  one 
to  three  days  generally  being  required  for  this  process.  The  parts  best 
adapted  to  examination  are  those  in  the  transitional  stage  of  violet  to  red. 

182.  This  procedure  has  been  subjected  to  innumerable  modifications  ; 
of  these,  the  most  used  are  :  ( i )  The  method  of  Lowit :  Small  pieces  are 
placed  in  a  solution  of  i   vol.   formic  acid  and  2  vols.    distilled  water 
until  they  have  become  transparent  (ten  minutes).    They  are  then  placed 
in  a  i  %  solution  of  gold  chlorid,  in  which  they  become  yellow  (one-quarter 
hour).      They  are    now  again   placed   in   formic   acid,    in  which  they 
pass  through  the  same  color  changes  as  above.      Finally,  they  are  washed 
and  teased,  or  subsequently  treated  with  alcohol  and  cut.      (2)  Ktihne 
(86)  acidifies  with  0.5%  solution  of  acetic  acid  (especially  in  the  case  of 
muscle),  then  treats  the  specimens  with  a  i%  solution  of  gold  chlorid, 
and  reduces  the  gold  with  20  to  25%  formic  acid  dissolved  in  equal  parts 
of  water  and  glycerin.     (3)  Ranvier  (89)  acidifies  with  fresh  lemon  juice 
filtered  through  flannel,  then  treats  with  a  i  %   solution  of  gold  chlorid 
(quarter  of  an  hour  or  longer),  and  finally  either  places  the  specimen  in 
water  acidulated  with  acetic  acid  (i  drop  to  30  c.c.  water)  and  subjects 
it    to    light    for   one    or   two    days,   or   reduces    it    in  the    dark,   as  in 
Lowit' s  method,  in  a  solution  of  i  vol.   formic  acid  and  2  vols.  water. 
(4)  Gerlach  uses  the  double  chlorid  of  gold  and  potassium,  but  in  weaker 
concentrations   than  a   i%   solution,   otherwise  he  continues  as  in  the 
method  of  Cohnheim.     (5)  Golgi  (94)  also  uses  the  same  double  chlorid, 
but  acidifies  with  0.5%  arsenious  acid,  and  then  reduces  in  i%  arseni- 
ous  acid  in  the  sunlight. 

183.  Gad  recommends  the  method  of  Chr.  Sihler  for  demonstrating 
the  nerve -endings  in  striated  muscle  :      Muscle  bundles  of  the  thickness 
of  a  goose  quill  are  first  placed  for  eighteen  hours  in  a  solution  composed 
of  acetic  acid  i  vol.,  glycerin  i  vol.,  and  i%  solution  of  chloral  hydrate 
6  vols.,  and  then  teased  in  pure  glycerin.     Afterward  they  are  placed  in  a 
mixture  of  Ehrlich's  hematoxylin  i  vol., glycerin  i  vol., and  i  °/c  chloral  hy- 
drate solution  6  vols. ,  in  which  the  specimens  are  allowed  to  remain  for  from 
three  to  ten  days.     The  pieces  are  now  placed  in  glycerin  acidified  with 
acetic  acid  (solution  No.  i),  in  which   the  color  becomes  differentiated, 
the  nerves  and  nerve-endings  in  the  muscles  and  vessels  being  deeply 
stained,  while  the  remaining  portion  of  the  specimen  becomes  decolor- 
ized.    After  having  stained  with  No.   2,  the  pieces  may  be  preserved  in 
pure  glycerin,  to  be  treated  later  with  acetic  acid  (solution  No.  i). 

These  methods  are  most  successful  in  reptilia  and  mammalia,  more 
difficult  in  the  other  classes  of  vertebrate  animals. 

The  gold-impregnation  of  the  nerve-endings  in  nonstriated  and 
heart  muscle  yields  less  reliable  results,  Golgi 's  chrome-silver  method 
or  the  Ehrlich  methylene-blue  method  being  better  (ind.  Technic  for 
Central  Nervous  System). 


SPECIAL  HISTOLOGY. 


I.  BLOOD  AND  BLOOD-FORMING  ORGANS,  HEART, 
BLOOD-VESSELS,  AND  LYMPH-VESSELS. 

A*  BLOOD  AND  LYMPH. 

J.  FORMATION  OF  BLOOD. 

EARLY  in  the  development  of  the  embryo  there  appear  in  a  por- 
tion of  the  extra-embryonic  area  of  the  blastoderm,  known  as  the 
area  vasculosa,  definite  masses  of  cells,  derived  from  the  mesen- 
chyme,  and  spoken  of  as  blood  islands,  which  are  intimately  connected 
with  the  formation  of  the  blood.  If  these  blood  islands  be  examined 
at  a  certain  stage,  free  cells  are  seen  lying  in  their  center,  appar- 
ently derived  from  the  central  cells  of  the  islands  ;  the  cells  sur- 
rounding them  represent  the  elements  which  later  go  to  form  the 
primitive  vascular  walls.  The  free  elements  are  the  first  blood-cells 
of  the  embryo.  The  blood-cells  thus  developed  enter  the  circula- 
tion by  means  of  blood  channels  formed  by  the  confluence  of  the 
blood  islands.  These  grow  toward  the  embryo  and  later  join  the 
large  central  vessels.  The  origin  of  these  blood  islands  is  still  an 
open  question.  Some  authors  contend  that  they  arise  from  the 
mesoblast  (P.  Mayer,  87,  93  ;  K.  Ziegler ;  van  der  Stricht,  92), 
others  that  they  are  of  entodermic  origin  (Kupfifer,  78  ;  Gensch ; 
Ruckert,  88  ;  C.  K.  Hoffmann,  93,  I ;  93,  II ;  Mehnert,  96).  At  a 
certain  period  the  embryonic  blood  consists  principally  of  nucleated 
red  cells,  which  proliferate  in  the  circulation  by  indirect  division. 
The  colorless  blood-cells,  the  development  of  which  is  not  yet  fully 
understood,  appear  later.  It  is  possible  that  they  also  are  elements 
of  the  blood  islands,  which  do  not  contain  any  hemoglobin.  In  a 
later  period  of  embryonic  life  the  liver  becomes  a  blood-forming 
organ.  Recent  investigations  have,  however,  shown  that  it  does 
not  take  a  direct  part  in  the  formation  of  the  blood,  but  only 
serves  as  an  area  in  which  the  blood-corpuscles  proliferate  during 
their  slow  passage  through  its  vessels.  The  blind  sac-like  endings 
of  the  venous  capillaries  seem  to  be  particularly  adapted  for  this 
purpose,  as  in  them  the  blood  current  stagnates,  and  it  is  here  that 
the  greater  number  of  blood-cells  reveal  mitotic  figures.  The 

168 


BLOOD    AND    LYMPH.  169 

newly  formed  elements  are  finally  swept  away  by  the  blood  stream 
and  enter  the  general  circulation  (van  der  Stricht,  92  ;  v.  Kostan- 
ecki,  92,  III).  Many  investigators  believe  that  the  red  blood-cells 
have  an  entirely  different  origin  in  the  liver — namely,  from  the  large 
polynuclear,  giant  cells,  which  are  thought  to  arise  either  from  the 
cells  of  the  capillaries  or  from  the  liver-cells  (Kuborn,  M.  Schmidt). 

Late  in  fetal  life  and  in  the  adult,  the  red  bone-marrow  and  the 
spleen  are  the  organs  which  form  the  red  blood-cells.  The  lym- 
phatic glands  and  the  spleen  produce  the  white  blood-cells.  In  ad- 
dition to  the  nucleated  red  corpuscles  which  are  present  up  to  a  cer- 
tain stage  of  development,  nonnucleated  red  blood-cells  also  appear. 
The  number  of  the  latter  increases,  until  finally  they  are  found 
almost  exclusively  in  the  blood  of  the  new-born  infant. 

The  blood  of  the  adult  consists  of  a  clear,  fluid,  coagulable  sub- 
stance, the  blood  plasma,  and  of  formed  elements  suspended  in  this 
intercellular  substance.  The  formed  elements  are  :  (a)  Red  blood- 
corpuscles  (erythrocytes)  ;  (/;)  white  blood-corpuscles  (leucocytes)  ; 
and  (<r)  the  blood  platelets  of  Bizzozero  (82),  Hayem.  Besides 
these,  there  are  present  particles  of  fat,  and,  as  H.  F.  Miiller  (96) 
has  recently  shown,  also  hemokonia. 


2.  RED  BLOOD-CORPUSCLES. 

In  man  and  nearly  all  mammalia  the  great  majority  of  the  red 
blood-corpuscles  are  nonnucleated,  biconcave  circular  discs  with 
rounded  edges.  They  have  smooth  surfaces,  are  transparent,  pale 
yellow  in  color,  and  very  elastic.  No  method  has  as  yet  been 
devised  to  demonstrate  a  nucleus  in  these  cells,  and  there  is  no 
doubt  that  the  red  blood-discs  of  the  human  adult  and  of  mammalia 
are  devoid,  in  the  histologic  sense,  of  a  nucleus  capable  of  differen- 
tiation (compare  Lavdowsky  ;  Arnold,  96).  They  are  therefore 
peculiarly  modified  cells. 

If  fresh  blood  be  left  for  some  time  undisturbed,  the  blood-discs 
adhere  to  each  other  by  their  flattened  surfaces,  grouping  them- 
selves in  rouleaux. 

By  certain  reagents  the  clear  and  transparent  contents  of  the 
blood-corpuscles  can  be  separated  into  two  substances — a  staining 
and  a  nonstaining.  The  first  consists  of  the  blood  pigment,  or 
hemoglobin,  which  can  be  dissolved  ;  the  second  of  a  colorless  sub- 
stance, the  stroma,  which  presents  itself  in  various  forms  (protoplasm 
of  the  cell). 

Hemoglobin  is  a  very  complex  proteid  which  may  be  decom- 
posed into  a  globulin  and  a  pigment  hematin.  The  hemoglobin  of 
the  majority  of  animals  crystallizes  in  the  form  of  rhombic  prisms  ; 
in  the  squirrel,  however,  in  hexagonal  plates,  and  in  the  guinea-pig 
in  tetrahedra.  Hematin  combines  with  hydrochloric  acid  to  form 
hemin,  or  Trichmanris  crystals,  of  brownish  color,  rhombic  shape, 
and  microscopic  size.  They  are  of  much  value  in  lego-medical 


I/O 


BLOOD  AND  BLOOD-FORMING  ORGANS. 


work,  since  they  may  be  obtained  from  blood,  no  matter  how  old, 
and  are  characteristic  of  hemoglobin.  They  may  be  obtained 
from  very  small  quantities  of  blood  pigment. 

The  stroma  probably  contains  the  hemoglobin  in  solution.  The 
question  as  to  whether  the  erythrocytes  possess  a  membrane  or  not 
is  difficult  to  answer,  although  in  all  probability  they  do  ( Lav- 
do  wsky). 

If  a  small  drop  of  blood  pressed  from  a  small  puncture  is 
placed  on  a  slide  and  covered  with  a  cover-glass,  the  red  blood- 
cells  soon  become  changed.  This  is  due  to  the  evaporation  of 
water  in  the  blood  plasma,  causing  an  increased  concentration  of 
the  sodium  chloride  contained,  which  in  turn  draws  water  from  the 
blood-cells  The  shrinkage  which  follows  produces  a  characteristic 


Fig.  145. — Hu- 
man red  blood-cells  ; 
X  !5oo  :  a,  As  seen 
from  the  surface  ;  b, 
as  seen  from  the  edge. 


Fig.  146. — So-called 
"rouleau"  formation  of 
human  erythrocytes ;  X 
1500. 


Fig.  147. — Hemin,  or 
Teichmann's  crystals,  from 
blood  stains  on  a  cloth. 


Fig.  148. — "  Crenated  "  human  red  blood-  Fig.  149.  — Red  blood-corpuscles  sub- 

cells  ;  X  I5°°-  jected  to  the  action  of  water  ;  X  I5°°  :  a, 

Spheric  blood-cell  ;  ^,  "blood  shadow." 

change  in  the  form  of  the  cells,  which  assume  a  crenated  or  stellate 
shape.  The  red  blood-cells  of  blood  mounted  in  normal  salt 
become  crenated  in  a  short  time  for  the  same  reason.  Red  blood- 
cells  are  variously  affected  by  different  fluids.  In  water  they  become 
spheric  and  lose  their  hemoglobin  by  solution.  Their  remains  then 
appear  as  clear,  spheric,  indistinct  blood  shadows,  which  may,  how- 
ever, be  again  rendered  distinct  by  staining  with  iodin.  Dilute 
acetic  acid  has  a  similar  but  more  rapid  action,  with  this  peculiarity, 
that  before  becoming  paler  the  blood-cells  momentarily  assume  a 
darker  hue.  Bile,  even  when  taken  from  the  animal  furnishing  the 
blood,  exerts  a  peculiar  influence  upon  the  red  blood-cells  ;  they 
first  become  distended,  and  then  suddenly  appear  to  explode  into 


BLOOD    AND    LYMPH. 


I/I 


small  fragments.  Dilute  solutions  of  tannic  acid  cause  the  hemo- 
globin to  leave  the  blood-cells,  and  coagulate  in  the  form  of  a  small 
globule  at  the  edge  of  the  blood-cell.  In  alkalies  of  moderate 
strength  the  red  blood-cells  break  down  in  a  few  moments. 

o 

Besides  the  disc-shaped  red  blood-cells,  every  well-made  prep- 
aration shows  a  few  small,  spheric,  nonnucleated  cells  containing 
hemoglobin.  These,  however,  have  received  as  yet  but  little 
attention. 


M.  Bethe  makes  the  statement  that  human  blood  and  the  blood  of 
mammalia  contain  corpuscles  of  different  sizes,  bearing  a  definite  numerical 
relationship  to  each  other.  "  If  they  be  classified  according  to  their  size, 
and  the  percentage  of  each  class  be  calculated,  the  result  will  show  a 
nearly  constant  proportional  graphic  curve  varying  but  slightly,  according 


5  c  c 


O 


Fig.  150. — Red  blood-corpuscles  from  various  vertebrate  animals  ;  X  looo  (Welker's 
model)  :  a,  From  proteus  (Olm)  ;  b,  from  frog  ;  c,  from  lizard  ;  d,  from  sparrow  ;  e,  from 
camel  ;  /"and^-,  from  man  ;  h,  from  myoxus  glis  ;  t,  from  goat ;  /£,  from  musk-deer. 


to  the  animal  species."  According  to  M.  Bethe,  dry  preparations  of 
human  and  animal  blood  may  be  distinguished  from  each  other,  with  the 
exception  of  the  blood  of  the  guinea-pig  which  presents  a  curve  identical 
with  that  of  human  blood. 

The  red  blood-cells  of  mammalia,  excepting  those  of  the  llama 
and  camel  species,  are  in  shape  and  structure  similar  to  those  of 
man.  The  red  blood-cells  of  the  llama  and  camel  have  the  shape 
of  an  ellipsoid,  flattened  at  its  short  axis,  but  also  nonnucleated. 

We  have  already  made  mention  of  the  fact  that  the  embryonal 
erythrocytes  are  nucleated  ;  the  question  now  arises  as  to  how,  in 
the  course  of  their  development,  they  lose  their  nuclei.  Three  pos- 
sibilities confront  us  :  First,  either  the  embryonal  blood-cells  are 
destroyed  and  gradually  replaced  by  previously  existing  nonnucle- 


1/2  BLOOD    AND    BLOOD-FORMING    ORGANS. 

ated  elements  ;  or,  second,  the  nonnucleated  red  cells  are  formed 
from  the  nucleated  by  an  absorption  of  the  nucleus  (or  what  appears 
to  be  such  to  the  eye  of  the  observer,  Arnold,  96)  ;  or,  finally,  the 
nucleus  is  extruded  from  the  original  nucleated  cell.  According  to 
recent  investigations  (Howell)  the  third  possibility  represents  the 
change  as  it  actually  takes  place. 

In  all  vertebrate  animals  except  mammalia,  the  red  blood- 
corpuscles  are  nucleated.  They  are  elliptic  discs  with  a  biconvex 
center  corresponding  to  the  position  of  the  nucleus.  The  blood- 
cells  of  the  amphibia  (frog)  are  well  adapted  for  study  on  account 
of  their  size.  They  are  long  and,  as  a  rule,  contain  an  elongated 
nucleus  with  a  coarse,  dense  chromatin  framework,  which  gives 
them  an  almost  homogeneous  appearance.  The  cell-body  may  be 
divided,  as  in  mammalia,  into  stroma  and  hemoglobin.  When  sub- 
jected to  certain  reagents,  the  contour  of  the  cells  appears  double 
and  sharply  defined.  This  condition  is,  however,  no  proof  of  the 
existence  of  a  membrane  ;  yet,  as  modern  observers  have  demon- 
strated, a  membrane  may  be  totally  or  partly  isolated  (Lavdow- 
sky).  The  blood-cells  of  birds,  reptiles  and  fishes  are  similarly 
constructed. 

The  diameter  of  the  erythrocytes  varies  greatly  in  different  ver- 
tebrate animals,  but  is  constant  in  each  species.  We  append  a  table 
of  their  number  in  a  cubic  millimeter  and  size  in  man  and  certain 
animals  as  compiled  by  Rollett  (71,  II)  and  M.  Bethe  : 

No.  IN 

SPECIES.  SIZE.  CUBIC  MILLI- 

METER. 

Man       (Homo] 7.2-7.8^ 5,000,000 

Monkey (Cercopith.  rtiber}      .    .  7  //       6,355,000 

Hare (Lepus  cuniculus}      .    .  7.16 6,410,000 

Guinea-pig (Cavia  cob.} 7-4-8 5j^59>5°° 

Dog (Canis  fam.} 7.2       6,650,000 

Cat (Felts  dom.} 6.2       9,900,000 

Horse (Emms  cab.} 5.58 7,403,500 

Musk-deer (Moschtis  jav .}   .    .    .    .2.5 

Spanish  goat (Capra  his.}  .    .    .  4.25 19,000,000 

Domestic  chaffinch  ....  (Fringilla  dom. )     .    .    .  Length,    11.9 

Breadth,     6.8 

Dove (Columba) L.  14.7     ....    2,010  ooo 

B.  6.5 

Chicken (Callus  dom.}     .    .    .    .  L.  12.1 

B.  7-2 

Duck (Anas  bosch.}      .    .    .    .  L.  12.9 

B.  8.0 

Tortoise ( Testudo grceca)      .    .    .  L.  21.2    ....        629,000 

B.  12.45 

Lizard (Lacerta  agil.}    .    .    .    .  L.  15.75  ....     1,292,000 

B.  9.1 

Snake (Colubernatr.}.    .    .    .  L.  22.0    ....        829,400 

B.  13.0 

Frog (Ranatemp.}     .    .    .    .  L.  22.3    ....        393>2O° 

B.  15.7 

Toad (Bufo  vulg.} L.  21.8    ....        389,000 

B.  15.9 

Triton (Triton  crist.}     .    .    .    .  L.  29.3    ....        103,000 

B.  19.5 


BLOOD    AND    LYMPH. 


173 


SPECIES. 

Salamander (Salamandra  mac.} 

{P rot  ens  atigu.) 

Sturgeon (Acipenser  St.]   .    . 

Carp {Cyprinus  Gobio}    . 


SIZE. 

.  Length,    37.8 
Breadth,  23.8 
.  L.  58 

B.  35 

.  L.  13.4 

B.  10.4 

.  L.  17.7 

B.  10.  i 


No.  IN 

CUBIC  MILLI- 
METER. 


8o,OOO 
35,ooo 


3.  WHITE  BLOOD-CORPUSCLES. 

The  white  blood-cells  contain  no  hemoglobin  and  are  nucleated 
elements  which,  under  certain  conditions,  possess  ameboid  move- 
ment. Their  size  varies  from  5  p.  to  10  p,  and  they  are  less  numer- 
ous than  the  red  blood-corpuscles,  one  white  blood-cell  to  from  three 
hundred  to  five  hundred  red  cells  being  a  normal  proportion.  In 


Fig.  151. — From  the  normal  blood  of  man  ;  X  I2O°  (from  dry  preparation  of  H. 
F.  Miiller)  :  a,  Red  blood-cell ;  b%  lymphocyte  ;  c  and  d,  mononuclear  leucocytes ;  *•, 
transitional  leucocyte  ;  f  and  £-,  leucocytes  with  polymorphous  nuclei. 

the  normal  blood  the  white  blood- cells  vary  in  shape,  and  the  fol- 
lowing varieties  are  distinguished:  (i)  Small  and  large  lympho- 
cytes ;  (2)  mononuclear  leucocytes  ;  (3)  transitional  leucocytes  ;  (4) 
leucocytes,  either  polymorphonuclear  or  polynuclear. 

The  lymphocytes  form  about  20%  of  the  white  blood-cells. 
They  vary  in  size  from  5  p.  to  7. 5  /JL  and  possess  a  relatively  large 
nucleus,  which  stains  rather  deeply,  surrounded  by  a  narrow  zone 
of  protoplasm. 

The  leucocytes  vary  in  size  from  7  p.  to  10/2.  The  mononuclear 
leucocytes,  constituting  about  2^  to  4%  of  the  white  blood-cells, 
have  a  nearly  round  or  oval  nucleus,  which  usually  does  not  stain 
very  deeply,  and  which  is  relatively  smaller  than  that  of  the  lymph- 
ocytes. The  transitional  leucocytes,  forming  also  about  2^  to 


174  BLOOD    AND    BLOOD-FORMING    ORGANS. 

4%  of  the  white  blood-cells,  are  developed  from  the  mononuclear 
variety  and  represent  transitional  stages  in  the  development  of 
mononuclear  leucocytes  to  those  with  polymorphous  nuclei.  The 
nucleus  in  the  transitional  form  is  similar  in  size  and  structure  to  that 
of  the  mononuclear  variety,  but  of  a  more  or  less  pronounced  horse- 
shoe-shape. The  leucocytes  with  polymorphous  nuclei,  developed 
from  the  transitional  forms,  are  very  numerous  in  the  blood,  form- 
ing about  70%  of  the  entire  number  of  white  blood-cells.  They 
are  also  the  cells  which  show  the  most  active  ameboid  movement 
when  examined  on  the  warm  stage.  They  possess  variously  lobu- 
lated  nuclei,  the  several  nuclear  masses  often  being  united  by  del- 
icate threads  of  nuclear  substance.  A  leucocyte  with  a  poly- 
morphous nucleus  becomes  a  polynuclear  cell  in  case  the  bridges 
of  nuclear  substance  uniting  the  several  lobules  of  the  nucleus  break 
through.  In  the  protoplasm  of  the  transitional  leucocytes,  the 
polymorphonuclear,  and  the  polynuclear  forms  are  found  fine  and 
coarse  granules.  Our  knowledge  of  these  granules  has,  however, 


a  e  p  y  6 

Fig.  152. — Ehrlich's  leucocytic  granules;  X  1800  (from  preparations  of  H.  F. 
Miiller)  :  a,  Acidophile  or  eosinophile  granules,  relatively  large  and  regularly  distributed  ; 
£,  neutrophile  granules  ;  j3,  amphophile  granules,  few  in  number  and  irregularly  dis- 
tributed ;  y,  mast  cells  with  granules  of  various  sizes  ;  d,  basophile  granules,  (a,  6,  and 
£,  From  the  normal  blood ;  y,  from  human  leukemic  blood ;  /3,  from  the  blood  of 
guinea-pig. ) 

been  greatly  extended  since  Ehrlich  has  shown  that  the  granules  of 
leucocytes  show  specific  reactions  toward  certain  anilin  stains,  or 
combinations  of  such  stains.  He  divides  the  granules  of  the  leuco- 
cytes into  five  classes  which  he  terms  respectively  «-,  /5-,  8-,  r-,  and  e- 
granules.  In  human  blood  are  found  the  a-granules,  which  show  an 
affinity  for  acid-anilin  stains,  are  therefore  known  as  acidophile  gran- 
ules, and,  since  they  are  most  readily  stained  in  eosin,  are  generally 
spoken  of  as  eosinophile  granules.  In  normal  blood  from  i  %  to  4^ 
of  the  polymorphonuclear  leucocytes  and  now  and  then  a  transi- 
tional cell  have  eosinophile  granules.  The  granules  are  coarse  and 
stain  bright  red  in  eosin.  Nearly  all  the  leucocytes  with  granules 
(from  65%  to  68%  of  all  white  blood-cells)  have  e -granules  or, 
since  they  are  stained  in  color  mixtures  formed  by  a  combination  of 
acid  and  basic  anilin  stains,  neutrophile  granules.  The  neutrophile 
granules  are  much  finer  than  the  eosinophile  and  are  not  stained 
in  acid  stains.  The  7-  and  ^-granules  are  stained  in  basic  anilin 
stains,  and  are  known  as  basophile  granules.  They  are  coarse  and 


BLOOD    AND    LYMPH.  1/5 

irregular,  and  the  leucocytes  containing  them  form  from  0.5^  to 
I  %  of  the  white  blood-cells. 

The  polymorphism  of  the  leucocyte -nucleus  has  induced  many 
investigators  to  advance  the  theory  that  a  direct  division  takes  place 
(fragmentation — Arnold,  Lowit).  Flemming  (91,  III),  however, 
succeeded  in  demonstrating  that  true  rnitotic  processes  actually  take 
place,  so  that  in  this  respect  there  really  exists  no  difference  between 
leucocytes  and  other  cells  (compare  also  H.  F.  Miiller,  89,  91).  It 
is  only  in  the  formation  of  polynuclear  leucocytes  that  the  poly- 
morphous nucleus  sometimes  undergoes  a  fragmentation  process 
which  results  in  several  parts.  But  even  in  this  case  pluripolar 
mitoses  have  been  observed.  A  division  of  the  cell-body  subse- 
quent to  that  of  the  nucleus  is  lacking  in  the  processes  just 
described.  As  a  result  a  single  cell  with  several  nuclei  is  formed 
(polykaryocyte).  The  fate  of  such  cells  is  still  in  doubt. 

The  extraordinary  motility  which  most  leucocytes  possess,  is  in 
great  part  responsible  for  their  wide  distribution,  even  outside  of 
the  vascular  system.  They  have  the  power  of  creeping  through 
the  walls  of  the  capillaries  (diapedesis,  Cohnheim  67,  I),  and  of 
penetrating  into  the  smallest  connective-tissue  clefts,  between  the 
cells  of  epithelia,  etc.,  whence  they  either  pass  on  (migratory  cells) 
or  remain  stationary  for  a  time.  An  important  function  falls  to  the 
lot  of  the  leucocytes  in  the  absorption  of  superfluous  tissue  particles 
or  in  the  removal  of  foreign  bodies  from  certain  regions  of  the  body. 
In  the  first  case  they  take  part  in  a  process  of  tissue-disintegration  ; 
in  the  second,  they  take  up  the  particles  by  means  of  their  pseudo- 
podia  for  the  purpose  either  of  assimilation  or  of  removal  (phago- 
cytes). It  may  be  readily  understood  that  the  latter  function  of  the 
leucocytes  is  of  the  greatest  importance  in  certain  pathologic  pro- 
cesses. 

It  is  somewhat  venturesome  at  the  present  state  of  our  knowl- 
edge to  make  definite  statements  as  to  the  origin  in  postembryonic 
life  of  the  various  forms  of  white  blood-cells  above  described.  The 
following  statement,  however,  seems  warranted  from  the  evidence 
at  hand. 

The  lymphocytes  would  seem  to  be  developed  in  the  meshes  of 
adenoid  tissue,  especially  in  the  so-called  germ  centers  of  Flemming, 
in  the  adenoid  tissue  of  lymph-glands  and  lymph-follicles  (see  under 
these).  Here  the  cells  undergo  active  karyokinetic  division,  but 
where  the  cells  which  pass  through  the  process  originate  is  a  matter 
concerning  which  there  is  a  difference  of  opinion.  Some  investi- 
gators believe  that  they  penetrate  the  germ  centers  with  the  lymph, 
and  find  there  a  suitable  place  for  division.  Again,  others  see  in 
Flemming's  germ  centers  permanent  organs  whose  elements  remain 
stationary  and  supply  the  blood  with  a  continuous  quota  of  lympho- 
cytes. Be  this  as  it  may,  the  fact  remains  that  the  germ  centers 
are  the  most  important  regions  for  the  formation  of  lymphocytes. 
From  these  they  pass  out  with  the  lymph  current  into  the  blood 


1/6  BLOOD    AND    BLOOD-FORMING    ORGANS. 

circulation,  there  to  enter  upon  the  functions  which  they  are  called 
upon  to  perform.  The  leucocytes  with  neutrophile  granules  are 
probably  developed  in  the  blood  and  lymph  from  mononuclear 
leucocytes  which  have  their  origin  in  the  spleen  pulp,  possibly  also 
in  the  bone-marrow.  The  leucocytes  of  circulating  blood  with 
eosinophile  granules  in  all  probability  come  from  mononuclear  cells 
with  such  granules  found  in  bone-marrow.  Under  certain  condi- 
tions it  would  seem  that  they  also  develop  in  connective  tissue. 
The  leucocytes  with  the  basophile  granules  probably  enter  the 
circulation  from  the  connective  tissue  of  certain  regions.  The 
lymphocytes  and  leucocytes  found  in  the  blood  are  also  found  in 
the  lymph-vessels  and  lymph-spaces. 


4.  BLOOD  PLATELETS  AND  BLOOD  PLASMA. 

The  third  element  of  the  blood  is  the  "  blood  platelets."  They 
are  extremely  delicate  and  transient  structures,  whose  existence  in 
the  living  blood  was  denied  for  a  long  time  by  many  investigators, 
but  whose  presence  in  the  wing  vessels  of  the  living  bat  was  conclu- 
sively demonstrated  by  Bizzozero  (84).  They  are  colorless  (free 
from  hemoglobin),  about  3  p.  in  diameter,  round,  and  are  separated 
by  treatment  with  a  iofG  saline  solution  into  a  hyaline  and  a  granu- 
lar substance.  No  more  can  be  said  about  the  function  of  these 
structures  than  that  they  have  to  do  with  the  coagulation  of  the 
blood.  They  are  present  in  the  blood  to  the  extent  of  about  two 
hundred  thousand  in  every  cubic  millimeter — i.  e.,  their  relation  to 
the  red  blood-cells  is  as  I  to  25  or  40.  The  genetic  relationship 
of  the  platelets  to  the  other  elements  of  the  blood  has  not  yet  been 
determined.  Hayem  regards  them  as  hematoblasts,  while  Arnold 
(96)  gives  to  them  an  erythrocytic  origin,  and  other  authors  consider 
them  the  remains  of  the  nuclei  of  broken-down  polynuclear  leuco- 
cytes, which  view  seems  most  in  accord  with  our  present  knowledge 
of  their  mode  of  development. 

H.  F.  Miiller  (96)  found  in  the  blood  of  healthy  and  diseased  indi- 
viduals highly  refractive,  colorless,  and  round  (seldom  rod-like)  bodies, 
which  he  terms  ' '  hemokonia. "  Their  numbers  vary,  although  they 
are  normal  constituents  of  the  blood.  Their  nature  and  origin  are  ob- 
scure. They  do  not  dissolve  in  acetic  acid,  nor  are  they  blackened  by 
osmic  acid.  The  latter  would  seem  to  indicate  that  they  do  not  consist 
of  ordinary  fat  substance,  although  they  are  probably  composed  of  a  sub- 
stance closely  allied  to  fat.  They  are  usually  i  fj.  in  diameter. 

The  fluid  medium  of  the  blood,  the  blood  plasma,  coagulates  on 
leaving  the  vessels.  It  may  even  undergo  the  same  process  within 
the  vessels  under  certain  abnormal  conditions.  As  a  result  an  in- 
soluble proteid  body,  "  fibrin,"  is  formed,  while  the  colorless 
elements  of  the  blood  are  in  part  destroyed  (Alexander  Schmidt). 


LYMPHOID    TISSUE,  LYMPH-NODULES,  AND    LYMPH -GLANDS.        1 77 

5,  BEHAVIOR  OF  BLOOD-CELLS  IN  THE  BLOOD  CURRENT, 

In  the  circulating  blood  the  behavior  of  the  formed  elements 
varies.  The  more  rapid  axial  current  contains  very  nearly  all  the 
erythrocytes,  and  as  a  consequence  very  few  are  found  adjacent  to  the 
walls  of  the  vessels.  In  the  peripheral  current,  on  the  other  hand, 
are  found  most  of  the  leucocytes,  and  in  a  retarded  circulation  they 
are  seen  to  glide  along  the  walls  of  the  vessels.  At  the  bifurcations 
of  the  vessels,  especially  of  the  capillaries,  the  erythrocytes  are 
sometimes  caught  and  elongated  by  the  division  of  the  current,  the 
one-half  of  the  cell  extending  into  the  one  and  the  other  half  into 
the  other  branch  of  the  vessel,  while  the  corpuscle  oscillates  back 
and  forth.  When  again  free  the  cell  immediately  resumes  its  original 
shape.  From  this  it  is  seen  that  erythrocytes  are  very  elastic 
structures.  In  the  smaller  vessels  and  capillaries,  especially  when 
the  latter  are  altered  by  pathologic  conditions,  the  leucocytes  may 
be  seen  passing  out  of  the  vessels,  and  it  would  seem  that  they  are 
able  to  penetrate  through  the  walls  and  even  through  the  endo- 
thelial  cells  lining  the  blood-vessels  (compare  also  Kolossow,  93). 
First,  they  send  out  a  fine  process,  which  is  probably  endowed  with 
a  solvent  action.  This  penetrates  the  wall  of  the  vessel,  after  which 
the  remainder  of  the  cell  pushes  its  way  through  slowly. 


B.  LYMPHOID  TISSUE,  LYMPH-NODULES,  AND  LYMPH- 
GLANDS. 

As  to  the  origin  of  lymphoid  tissue,  the  lymph-glands,  and  the 
spleen,  there  is  still  considerable  difference  of  opinion.  Most 
authors  believe  that  these  structures  are  developed  from  the  middle 
germinal  layer  (Stohr,  89  ;  Paneth  ;  J.  Schaffer,  91  ;  Tomarkin). 
Others  believe  in  an  entodermic  origin  (Kupffer,  92  ;  Retterer ; 
Klaatsch  ;  C.  K.  Hoffmann,  93,  II). 

The  framework  of  lymphoid  tissue  is  a  reticular  connective  tis- 
sue (adenoid  connective  tissue — His,  61).  This  consists  of  a  net- 
work of  fine  fibrils  and  of  branched  connective-tissue  cells.  Within 
its  meshes  the  lymph-cells  lie  in  such  numbers  and  so  densely  ar- 
ranged that,  on  microscopic  examination  the  network  is  entirely 
covered.  Special  methods  are  therefore  necessary  to  bring  out  the 
structure  of  the  latter.  Lymph  tissue  may  be  diffuse,  as  in  the 
mucous  membrane  of  the  air-passages  and  as  in  that  of  the  intes- 
tinal tract,  uterus,  etc.  (vid.  Sauer,  96). 

Lymphoid  tissue  may  be  also  sharply  defined  in  the  form  of  round 
nodules,  simple  follicles  or  nodules.  These  are  either  single,  solitary 
lymph-follicles,  or  gathered  into  groups,  agmiuatcd  lymph-nodules. 
They  are  found  scattered  in  the  mucous  membrane  of  the  mouth, 
pharynx,  and  intestine.  In  lymph-nodules  also  we  find  the  charac- 
teristic lymph-cells  and  the  adenoid  reticulum.  As  a  rule,  the  former 

12 


\ 


178 


BLOOD    AND    BLOOD-FORMING    ORGANS. 


are  arranged  concentrically  at  the  periphery  ;  and  in  the  center  of 
the  nodule  the  reticular  tissue  usually  has  wider  meshes,  and  the 
lymph-cells  are  less  densely  placed.  (Fig.  153.)  In  the  center  of 
the  nodule  the  cells  often  show  numerous  mitoses,  and  it  is  here 
that  an  active  proliferation  of  the  cells  takes  place.  The  cells  may 
either  remain  in  the  lymph-follicle  or  the  newly  formed  cells  are 
pushed  to  the  periphery  of  the  nodule,  and  are  then  swept  into  the 
circulation  by  the  slow  lymph  current  which  circulates  between  the 
wide  meshes  of  the  reticular  connective  tissue.  Flemming  (85,  II) 
has  called  that  central  part  of  the  nodule  containing  the  proliferating 
cells  the  germ  center  or  secondary  nodule  (compare  p.  175).  The 
germ  centers  are  transitory  structures,  and  are  consequently  found 
in  different  stages  of  development.  They  may  even  be  absent  for  a 
time. 


Gland. 


Submu- 
cosa. 


Fig.  153. — A  solitary  lymph-nodule  from  the  human  colon.    At  a  is  seen  the  pronounced 
concentric  arrangement  of  the  lymph-cells. 


The  lymph-glands  are  organs  of  a  more  complicated  structure, 
but  also  consist  of  lymphoid  tissue.  They  are  situated  here  and  there 
in  the  course  of  the  lymph-vessel  and  are  widely  distributed.  Their 
size  varies  greatly.  In  shape  they  are  much  like  a  bean  or  kidney, 
and  the  indentation  on  one  side  is  known  as  the  hilum.  The  affer- 
ent lymph-vessels,  the  vasa  afferentia,  enter  at  the  convex  surface 
of  the  organ,  while  the  efferent  vessels,  the  vasa  effcrcntia,  pass  out 
at  the  hilum.  The  whole  gland  is  surrounded  by  a  capsule  consist- 
ing of  two  layers  :  the  outer  is  made  up  of  a  loose,  and  the  inner  of 
a  more  compact,  connective  tissue  in  which  a  few  smooth  muscle- 
fibers  are  imbedded.  Portions  of  the  inner  layer  pass  into  the  sub- 
stance of  the  gland  to  form  septa,  or  trabcculce.  by  means  of  which 
the  organ  is  divided  into  a  number  of  imperfectly  separated  compart- 


LYMPHOID    TISSUE,   LYMPH-NODULES,  AND    LYMPH-GLANDS. 

ments.  The  lymphoid  substance  of  the  gland  is  so  distributed  that 
at  its  periphery  a  large  number  of  lymph-nodules  are  placed  in 
dense  masses  separated  from  each  other  by  the  trabeculae  just  de- 
scribed, the  cortical  nodules.  The  nodules  are  identical  in  struc- 
ture with  those  mentioned  above.  They  form  a  peripheral  layer 
which  is,  however,  not  clearly  defined  in  the  neighborhood  of  the 
hilum.  This  layer  is  known  as  the  cortex  of  the  lymph-gland. 
(Fig.  154.)  The  lymphoid  tissue  of  the  interior  of  the  gland,  the 
medullary  substance,  is  in  the  shape  of  cords — medullary  cords. 
These  connect  with  each  other  and  form  a  network  of  lymphoid 
tissue,  in  the  open  spaces  of  which  lie  the  trabeculae.  At  their 
periphery  the  nodules  and  medullary  cords  gradually  pass  into  a 
wide-meshed  lymphatic  tissue,  the  lymph-sinus  of  the  gland,  parts 
of  which  lie  (i)  between  the  capsule  and  the  cortical  substance,  (2) 
between  the  nodules  of  the  latter  and  the  trabeculae,  (3)  between 
the  medullary  cords  and  the  trabeculae,  and  (4)  between  the  medul- 

Blood-vessels.  a        b 


Trabecula. 

Fig.  154. — Section  through  a  mesenteric  lymph-gland  of  cat,  with  injected  blood-vessels ; 
X  50  :  a,  Medullary  substance  ;  b,  cortical  substance  with  cortical  nodules. 

lary  substance  and  the  capsule  at  the  hilum.  The  sinus  is  therefore 
intimately  connected  not  only  with  the  capsule,  but  also  with  the 
trabeculae.  At  the  hilum  the  loose  lymphoid  tissue  represents  a 
terminal  sinus  (Toldt). 

The  inner  wall  of  the  capsule  and  the  trabecuLt  with  their  pro- 
cesses are  covered  by  flattened  endothelial  cells  which  are  continu- 
ous with  those  of  the  afferent  and  efferent  lymph-vessels.  The 
lymph  flows  into  the  gland  through  the  afferent  vessels,  and  passes 
along  into  the  interior  through  the  spaces  offering  the  least  resist- 
ance (sinuses).  The  latter  represent  those  peripheral  portions  of 
the  nodules  and  of  the  medullary  cords  in  which  the  lymphoid  tissue 
is  present  in  loose  arrangement.  The  lymph  consequently  envelops 
not  only  the  lymph-nodules  of  the  cortical  substance,  but  also  the 
medullary  cords,  and  finally  streams  into  the  terminal  sinus  and 


i8o 


BLOOD    AND    BLOOD-FORMING    ORGANS. 


then  into  the  efferent  channels.  As  a  result  the  lymph  takes  with 
it  the  newly  formed  cells  of  the  lymph-nodules  and  the  medullary 
cords,  and  passes  out  much  richer  in  cellular  elements  than  on  its 
entrance. 

A  large  number  of  arterial  blood-vessels  enter  the  lymph-gland 
through  the  hilum  and  penetrate  into  the  interior  of  the  organ 
through  the  trabeculae.  After  passing  through  the  sinuses  they 
break  up  into  capillaries  in  the  medullary  cords  or  in  the  lymph- 
nodules  of  the  cortical  substance.  The  sinuses,  then,  contain  no 


Mitosis. 


Germ  center. 


s Lymph-sinus. 


Medullary 
cord.. 


Fig.  155. — From  a  human  lymph-gland;    X   24°-     At  a    are    seen  the  concentrically 
arranged  cells  of  the  lymph-nodules.      (Fixation  with  Flemming's  fluid.) 

capillaries.  The  arterial  capillaries  pass  over  into  the  venous  capil- 
laries, and  the  veins  resulting  from  the  union  of  the  latter  pass  to 
the  periphery  of  the  organ  side  by  side  with  the  arteries. 


C  THE  SPLEEN. 

The  spleen  is  a  blood-forming  organ,  in  which  white  blood-cells 
and,  in  embryonic  life  and  under  certain  conditions  in  adult  life  also, 
red  blood-cells  are  formed — the  former  in  the  adenoid  tissue  (Mal- 
pighian  corpuscles)  and  spleen  pulp,  the  latter  only  in  the  spleen 
pulp. 

The  spleen  is  covered  by  peritoneum,  and  possesses  a  capsule 


THE    SPLEEN. 


181 


consisting  of  connective  tissue,  elastic  fibers,  and  nonstriated  muscle- 
cells.  This  capsule  sends  numerous  processes  or  trabeculae  into 
the  interior  of  the  organ,  which  branch  and  form  a  framework  in 
which  the  vessels,  especially  the  veins,  are  imbedded.  This  con- 
nective-tissue framework  breaks  up  to  form  the  reticular  tissue 
which  constitutes  the  ground  substance  of  the  spleen. 

On  examining  a  section  of  the  spleen  with  the  low-power  mag- 
nifying glass,  sections  of  the  trabeculae,  and  round  or  oval  masses 
of  cells,  having  a  diameter  of  about  0.5  mm.,  and  in  structure  and 


-  Blood-vessel. 
i-Trabecula. 


Trabecula. -•"&:--     ;i«:S 


Spleen  pulp. 


Artery. 


Malpighian  cor- 
puscle     with 
germ  center. 


Fig.  156. — Part  of  a  section  through  the  human  spleen;   X  75-      (Sublimate  fixation.) 
At  a  is  an  oblong  Malpighian  body  with  a  blood-vessel. 


appearance  similar  to  the  lymph-nodules  (Malpighian  corpuscles), 
are  clearly  defined  ;  between  and  around  these  structures  is  a  tissue 
rich  in  cells,  blood-vessels  and  blood-corpuscles,  known  as  the 
spleen  pulp. 

The  organ  has  a  very  typical  blood  supply.  Its  arteries  enter 
at  the  hilum,  or  indented  surface,  and  its  veins  pass  out  at  the  same 
place.  On  the  penetration  of  the  vessels  through  the  capsule,  the 
latter  forms  sheaths  around  them  (trabeculae),  but  as  soon  as  the 
arteries  and  veins  separate,  the  trabeculae  envelop  the  veins  alone. 


1 82  BLOOD    AND    BLOOD-FORMING    ORGANS. 

The  arteries  break  up  into  smaller  branches,  which  in  turn  divide 
into  a  large  number  of  tuft-like  groups  of  arterioles.  Soon  after  their 
separation  from  the  veins,  the  adventitia  (outer  fibrous  tissue  coat)  of 
the  arteries  begins  to  assume  a  lymphoid  character.  This  lymphoid 
tissue  increases  here  and  there  to  form  true  lymphoid  nodules,  pos- 
sessing all  the  characteristics  already  mentioned — reticular  tissue, 
germ  centers,  etc.  These  are  the  Malpighian  bodies,  or  corpuscles  ; 
they  are  not  very  plentifully  represented  in  man.  The  Malpighian 
bodies  with  their  germ  centers  are  formative  centers  for  the  lympho- 
cytes. The  newly  formed  cells  pass  into  the  pulp  and  mix  with  its 
elements,  which  are  then  bathed  by  the  blood  emptying  from  the 
arterial  capillaries  into  the  channels  of  the  pulp.  The  lymphoid 
sheaths  and  nodules  derive  their  blood  supply  from  arteries  which 
arise  from  the  lateral  branches  of  the  splenic  vessels,  and  which 
divide  into  capillaries  inside  of  the  lymph  sheaths  or  nodules,  and 
only  assume  a  venous  character  outside  of  the  lymphoid  substance. 
These  vessels  constitute  the  nutritive  vascular  system  of  the  spleen. 

The  small  arterial  branches  above  mentioned  break  up  into  very 
fine  arterioles  which  gradually  lose  their  lymphoid  sheath,  so  that 
branches  with  a  diameter  of  0.02  mm.  no  longer  possess  a  lymphoid 
sheath,  but  again  assume  an  adventitia  of  the  usual  type.  The 
smallest  arterioles  now  pass  over  into  capillaries  which  are  for  a 
time  accompanied  by  the  adventitia  (capillary  sheath),  while  the 
terminal  branches  have  the  usual  structure  of  the  capillary  wall  and 
are  gradually  lost  in  the  meshes  of  the  pulp.  (See  below.)  On  the 
other  hand,  the  beginnings  of  the  venous  capillaries  may  be  dis- 
tinctly seen  in  the  pulp  spaces.  Groups  of  these  capillaries  com- 
bine to  form  larger  vessels,  which,  however,  still  retain  a  capillary 
structure,  and  these  again  form  small  veins  which  unite  to  form  the 
larger  veins. 

F.  P.  Mall, whose  recent  contributions  on  the  structure  of  the  spleen 
have  greatly  extended  our  knowledge  of  the  microscopic  anatomy  of 
this  organ,  states  that  the  trabecular  and  vascular  systems  together 
outline  masses  of  spleen  pulp  about  I  mm.  in  diameter,  which  he  has 
named  spleen  lobules.  Each  lobule  is  bounded  by  three  main  in- 
terlobular  trabeculae,  each  of  which  sends  three  intralobular  trabe- 
culae  into  the  lobule  which  communicate  with  each  other  in  such  a 
manner  as  to  divide  the  lobule  into  about  ten  smaller  compartments. 
An  artery  enters  at  one  end  of  the  lobule  and,  passing  up 
through  its  center,  gives  off  a  branch  to  the  spleen  pulp  found  in 
each  of  the  ten  compartments  formed  by  the  intralobular  trabeculae. 
The  spleen  pulp  in  these  compartments  is  arranged  in  the  form  of 
anastomosing  columns,  or  cords,  to  which  Mall  has  given  the  name 
of  pulp  cords.  The  branches  of  the  main  intralobular  artery,  going 
to  each  compartment,  divide  repeatedly  ;  the  terminal  branches 
course  in  the  spleen-pulp  cords,  and  in  their  path  give  off  numerous 
small  side  branches  which  end  in  small  expansions  known  as  the 
ampulla  of  Thoma.  "  The  first  two-thirds  of  the  ampulla  are  lined 


THE    SPLEEN. 


with  spindle-shaped  cells  lying  on  a  delicate  framework  of  reticulum. 
Through  the  last  third,  at  the  junction  with  the  vein,  no  cell  bound- 
aries can  be  demonstrated.  In  fact,  it  appears  as  if  this  portion  of 
the  ampulla  were  cut  up  by  fibrils  of  the  reticulum  passing  across 
it"  (F.  P.  Mall).  The  veins  of  the  lobule  begin  in  a  system  of  venous 
spaces  surrounding  the  pulp  cords.  These  are  in  communication 
with  intralobular  veins,  often  associated  with  intralobular  trabeculae, 
and  the  latter  empty  into  the  interlobular  veins  found  in  some  of  the 
interlobular  trabeculae.  F.  P.  Mall  further  states  that  "the  ampullae 
and  venous  plexus  have  very  porous  walls,  which  permit  fluids  to 
pass  through  with  great  ease  and  granules  only  with  difficulty.  In 
life  the  plasma  constantly  flows  through  the  intercellular  spaces  of  the 
pulp  cords,  while  the  blood-corpuscles  keep  within  fixed  channels." 
The  accompanying  diagram  (Fig.  157),  slightly,  though  immate- 


i 

I  Capsule. 


Intralobular  venous 

spaces. 
•  Intralobular  vein. 


•  Ampulla  of  Thoma. 

—  Spleen  pulp  cord. 

—  Interlobular  vein. 

-—  Intralobular  vein. 


Intralobular  trabecula.  -  - 


Artery  to  one  of  the  ten 
compartments. 


Intralobular  artery. 
Interlobular  trabecula. 


Intralobular  trabecula. , 


Malpighian  corpuscle. 


Fig-  157- — Diagram  of  lobule  of  the  spleen  (Mall,  "  Johns  Hopkins  Hospital 
Bulletin,"  Sept.,  Oct.,  1898). 

rially,  modified  from  one  given  by  Mall,  shows  clearly  the  trabecular 
and  vascular  systems  of  a  spleen  lobule. 

In  larger  spleens  there  may  be  some  two  hundred  thousand  of 
these  lobules.  In  a  dog  weighing  10  kg.  there  are  on  an  average 
some  eighty  thousand  (F.  P.  Mall). 

The  splenic  pulp  consists  of  a  very  delicate  reticulum,  in  the 
meshes  of  which  are  found  (i)  fully  developed  red  blood-cells  ;  (2) 
now  and  then  nucleated  red  blood-cells  ;  (3)  in  many  animals  giant 
cells  ;  (4)  cells  containing  red  blood-corpuscles  and  the  remains  of 
such,  with  or  without  pigment  ;  (5)  the  different  varieties  of  white 
blood-cells,  especially  a  relatively  large  proportion  of  mononuclear 
leucocytes.  Pigment  granules,  either  extra-  or  intracellular,  also 
occur  in  the  splenic  pulp.  The  pigment  probably  originates  from 
disintegrating  erythrocytes.  Besides  these  are  found,  especially  in 


1 84 


BLOOD   AND    BLOOD-FORMING    ORGANS. 


teased  preparations,  long,  spindle-shaped  and  flat  cells,  which  are 
probably  derivatives  of  the  connective-tissue  cells  of  the  pulp  and  of 
the  endothelium  and  muscular  fibers  of  the  vessels. 


Fig.  158. — Cells  containing  pigment,  blood-corpuscles,  and  hemic  masses  from  the 
spleen  of  dog;   X  1800  (from  cover-glass  of  H.  F.  Miiller). 


_  b 


Fig.  159. — From  the  human  spleen  ;   X  80  (chrome-silver  method)  :  a,  Larger  fibers 
of  a  Malpighian  body  ;  l>,  reticular  fibrils  (Gitterfasern). 

In  embryonic  life  and  under  certain  conditions  in  postembryonic 
life  (after  severe  hemorrhage  and  in  certain  diseases)  red  blood-cells 
are  developed  in  the  spleen  pulp.  The  nucleated  red  blood-cells 


THE    BONE-MARROW.  185 

from  which  they  develop  may  lose  their  nuclei  in  the  spleen  pulp 
or  only  after  entering  the  circulation  (compare  Bone-marrow). 

By  means  of  certain  methods,  especially  the  chrome-silver 
method  (Oppel,  91),  a  very  delicate  reticular  network — /.  e.,  that 
surrounding  the  capillary  walls — may  be  brought  to  view  in  the 
spleen.  The  fibers  composing  it  have  been  called  by  Kupffer  retic- 
ular fibers. 

The  spleen  receives  medullated  and  nonmedullated  nerve-fibers  ; 
the  latter  are  much  more  numerous.  The  medullated  nerve- 
fibers  are  no  doubt  the  dendrites  of  sensory  neurones.  Their 
mode  of  ending  has,  however,  not  been  determined.  It  is  probable 
that  they  will  be  found  to  terminate  in  the  fibrous-tissue  coat  of  the 
vessels,  and  in  the  trabeculae  and  capsule.  The  nonmedullated 
nerve-fibers,  no  doubt  the  neuraxes  of  sympathetic  neurones,  are 
very  numerous  ;  they  enter  the  spleen  with  the  artery  and  mainly 
follow  its  branches.  By  means  of  the  chrome-silver  method, 
Retzius  (92)  has  shown  that  in  the  rabbit  and  mouse  these  nerve- 
fibers  follow  the  vessels,  forming  plexuses  which  surround  them, 
the  terminal  branches  of  these  plexuses  terminating  in  free  endings 
in  the  muscular  coat  of  the  arteries.  Here  and  there  a  nerve-fiber 
could  be  traced  into  the  spleen  pulp.  The  mode  of  ending  of  such 
fibers  could,  however,  not  be  determined.  The  nonstriated  muscle- 
cells  of  the  trabeculae  and  capsule  no  doubt  also  receive  their  inner- 
vation  from  the  nonmedullated  nerves  (neuraxes  of  sympathetic 
neurones). 

D.  THE  BONE-MARROW* 

The  ingrowing  periosteal  bud  which  ushers  in  the  process  of 
endochondral  ossification  constitutes  the  first  trace  of  an  embryonal 
bone-marrow  (compare  p.  108).  It  consists  mainly  of  elements 
from  the  periosteum  which  penetrate  with  the  vascular  bud  and  later 
form  the  entire  adult  bone-marrow.  The  red  bone-marrow  is  formed 
first.  This  is  present  in  embryos  and  young  animals,  and  is  devel- 
oped from  the  above  elements  during  the  process  of  ossification. 
As  Neumann  (82)  has  shown,  the  red  bone-marrow  of  the  human 
embryo  is  first  formed  in  the  bones  of  the  extremities  and  gradually 
replaced  in  a  proximal  direction,  so  that  in  the  adult  it  is  found 
only  in  the  proximal  epiphyses,  in  the  flat  bones  and  in  the 
bodies  of  the  vertebrae.  In  the  remaining  bones  and  parts  of  bones 
the  red  bone-marrow  is  replaced  by  the  yellow  bone-marrow  (fat- 
marrow). 

As  a  result  of  hunger  and  certain  pathologic  conditions  the  yel- 
low bone-marrow  changes  into  a  gelatinous  substance,  which,  how- 
ever, may  again  assume  its  original  character. 

The  red  bone-marrow,  surrounded  by  a  delicate  fibrous-tissue 
membrane,  the  endosteum,  is  a  tissue  consisting  of  various  cellu- 
lar elements  imbedded  in  a  matrix  of  reticular  tissue,  similar  to  the 


1 86  BLOOD    AND    BLOOD-FORMING    ORGANS. 

adenoid  reticulum.  Aside  from  these  cellular  elements,  the  marrow 
contains  numerous  vessels  (see  below),  fixed  connective-tissue  cells, 
etc. 

The  typical  cellular  elements  of  red  bone-marrow  are  : 
I.  The  Marrow-cells,  or  Myelocytcs. — These  are  cells,  slightly 
larger  than  the  leucocytes,  possessing  a  relatively  large  nucleus  of 
round  or  oval  shape,  rarely  lobular,  containing  a  relatively  small 
amount  of  chromatin.  In  the  protoplasm  of  these  cells  are  found 
(in  man)  neutrophile  granules  and  now  and  again  small  vacuoles. 
They  are  said  to  contain  various  pigment  granules.  These  cells 
are  not  found  in  normal  blood,  but  are  found  in  circulating  blood  in 
certain  forms  of  leukemia,  where  they  may  be  distinguished  from 
the  mononuclear  leucocytes  partly  by  their  structure,  more  particu- 


Fig.  160.  —  Cover-glass  preparation  from  the  bone  marrow  of  dog;  X  1200  (from 
preparation  of  H.  F.  Miiller)  :  a,  Mast-cell  ;  6,  lymphocyte  ;  c,  eosinophile  cell  ;  d,  red 
blood-cell  ;  e,  erythroblast  in  process  of  division  ;  /,  /,  normoblast  ;  g,  erythroblast. 
Myelocyte  not  shown  in  this  figure. 


larly   by   the  presence   of  neutrophile   granules    not   found  in  the 
mononuclear  leucocytes. 

2.  Nucleated  Red  Blood-cells  containing  Hemoglobin.  —  Two 
varieties  of  these  cells  are  recognized  structurally,  with  interme- 
diary stages,  as  one  variety  is  developed  from  the  other.  The 
erythroblasts,  being  genetically  the  earlier  cells,  possess  relatively 
large  nuclei  with  distinct  chromatin  network,  surrounded  by  a 
protoplasm  tinged  with  hemoglobin,  and  are  often  found  in  a  stage 
of  mitosis.  The  other  variety  of  nucleated  red  blood-cells,  the 
normoblasts,  are  developed  from  the  erythroblasts.  They  contain 
globular  nuclei,  staining  deeply,  in  which  no  chromatin  network 
is  recognizable,  and  surrounded  by  a  layer  of  protoplasm  containing 
hemoglobin.  The  normoblasts  are  changed  into  the  nonnucleated 


THE    BONE-MARROW. 


l8/ 


red  blood-discs  by  the  extrusion  of  the  nucleus.  This  process 
occurs  normally  in  the  red  bone-marrow,  or  in  the  venous  spaces 
of  the  bone-marrow  (see  below).  In  certain  pathologic  conditions, 
nucleated  red  blood-cells  are  found  in  the  circulation. 

3.  Cells  with  Eosinophile  Granules.  —  In  the  red  bone-marrow 
are  found  numerous  eosinophile  (acidophile)  cells,  some  with  round  - 
or  oval  nuclei  (mononuclear  eosinophile  cells),  others  with  horse- 
shoe-shaped nuclei  (transitional  eosinophile  cells),  and  still  others 
with  polymorphous  nuclei.  The  latter,  which  are  the  most  numer- 
ous, are  no  doubt  the  mature  cells,  and  are  identical  with  those 
elements  of  the  blood  having  the  same  structure. 


:  „ 


<© 


\ 


Fig.  161. — From  a  section  through  human  red  bone-marrow  ;  X  680.  Technic 
No.  216  :  a,  f,  Normoblasts  ;  b,  reticulum  ;  c,  mitosis  in  giant  cell ;  </,  giant  cell  ;  e,  h, 
myelocytes  ;  gy  mitosis  ;  z,  space  containing  fat-cells. 


4.  The  various  forms  of  leucocytes  and  the  lymphocytes  found  in 
blood  and  lymph. 

5.  The  giant  cells  (myeloplaxes),  which  are  situated  in  the  center 
of  the  marrow,   and    contain  simple  or   polymorphous  nuclei,   or 
lie  adjacent  to  the  bone  in  the  form  of  osteoclasts,  which  are,  as  a 
rule,  polynuclear  (compare  p.  ill).      The  physiologic  significance 
of  the  giant  cells  is  still  obscure.     They  probably  originate  from 
single  leucocytes  by  an  increase  in  size  of  the  latter,  and  not,  as 
many  assume,  from  a  fusing  of  several  leucocytes.     The  giant  cells 
are  endowed  with  ameboid  movement,  and  often  act  as  phagocytes 
(the  latter  quality  is  denied  them  by  M.  Heidenhain,  94). 


1 88  BLOOD    AND    BLOOD-FORMING    ORGANS. 

M.  Heidenhain  (94)  has  made  a  particular  study  of  the  giant 
cells.  According  to  him  the  nuclei  of  these  cells  take  the  form  of  per- 
forated hollow  spheres  whose  thick  walls  contain  "endoplasm."  The 
latter  is  continuous  with  the  remaining  protoplasm  of  the  cell,  the  "  exo- 
plasm  "  through  the  "perforating  canals"  of  the  nuclear  wall.  The 
exoplasm  is  arranged  in  three  concentric  layers,  separated  from  each 
other  by  membranes,  the  external  membrane  of  the  outer  zone  being  the 
membrane  of  the  cell.  The  outer  layer  or  marginal  zone  is  of  a  transient 
nature,  but  is  always  renewed  by  the  cell.  Thus,  the  cell -membrane  is 
replaced  by  the  secondary  membrane  situated  between  the  second  and 
third  zone.  According  to  the  same  author  the  functions  of  the  giant 
cells  appear  to  consist  in  "  the  selection  and  elaboration  of  certain  albu- 
minoid substances  of  the  lymph  and  blood  currents,  which  are  later 
returned  to  the  circulation. ' '  The  number  of  centrosomes  occurring  in 
the  mononuclear  giant  cells  of  the  bone-marrow  is  very  large,  and  in 
some  cases,  as  in  a  pluripolar  mitosis,  may  even  exceed  one  hundred  in 
number. 

The  distribution  of  the  blood-vessels  in  the  bone-marrow  is  as 
follows  :  On  entering  the  bone  the  nutrient  arteries  divide  into  a 
large  number  of  small  branches,  which  then  break  up  into  small 
arterial  capillaries.  The  latter  pass  over  into  relatively  large  venous 
capillaries,  whose  walls  either  finally  disappear  entirely  or  are  broken 
through  in  many  places  so  that  the  venous  blood  pours  into  the 
spaces  of  the  red  bone-marrow  where  the  current  is  very  slow.  The 
blood  passes  out  by  means  of  smaller  veins  formed  by  the  conflu- 
ence of  the  capillaries  which  collect  the  blood  from  the  marrow.  It 
is  worth  mentioning  that  the  venous  vessels,  while  inside  of  the 
bone-marrow,  possess  no  valves  ;  but,  on  the  other  hand,  they 
have  an  unusually  large  number  of  valves  immediately  after  leaving 
the  bone. 

Yellow  bone-marrow  is  derived  from  red  bone-marrow  by  a 
change  of  the  marrow-cells  into  fat-cells.  The  gelatinous  marrow, 
on  the  contrary,  is  characterized  by  the  small  quantity  of  fat  which 
it  contains.  Neither  the  yellow  nor  the  gelatinous  bone-marrow  is 
a  blood-forming  organ  (compare  Neumann,  90;  Bizzozero,  91  ; 
H.  F.  Miiller,  91  ;  van  der  Stricht,  92). 


E.  THE  THYMUS  GLAND. 

The  thymus  gland  is  usually  considered  as  belonging  to  the 
lymphoid  organs,  although  in  its  earliest  development  it  resembles 
an  epithelial,  glandular  structure.  In  the  epithelial  stage,  this  gland 
develops  from  the  entoderm  of  the  second  and  third  gill  clefts. 
Mesodermic  cells  grow  into  this  epithelial  structure,  proliferate  and 
then  differentiate  into  a  tissue  resembling  adenoid  tissue.  It  retains 
this  structure  until  about  the  end  of  the  second  year  after  birth,  when 
it  slowly  begins  to  retrograde  into  a  mass  of  fibrous  tissue,  adipose 
tissue,  and  cellular  debris,  which  structure  it  presents  in  adult  life. 


THE    THYMUS    GLAND. 


By  means  of  connective-tissue  septa,  the  thymus  is  divided  into 
larger  lobes,  and  these  again  into  smaller  lobes,  until  finally  a 
number  of  very  small,  almost  spheric  structures  are  formed — the 
lobules  of  the  gland.  These  consist  of  a  reticular  connective  tissue 
much  more  delicate  at  the  periphery  than  at  the  center  of  the 


.ill 


Fig.  162. — A  small  lobule  from  the  thymus  of  child,  with  well-developed  cortex, 
presenting  a  structure  similar  to  that  of  the  cortex  of  a  lymph- gland  ;  X  °°  :  a, 
Hilus ;  ^,  medullary  substance  ;  <:,  cortical  substance  ;  d,  trabecula. 

lobule.  In  the  meshes  of  the  reticular  tissue  are  cellular  elements, 
in  structure  similar  to  the  lymphocytes,  which  are  more  numerous 
at  the  periphery  of  the  lobule  than  at  its  center,  so  that  we  may 
here  speak  of  the  lobule  as  divided  into  a  cortical  and  a  medullary 
portion.  The  latter  is  usually  entirely  surrounded  by  the  cor-' 
tical  substance,  but  may  pene- 
trate to  the  periphery  of  the 
lobule,  allowing  the  blood-ves- 
sels to  enter  and  leave  at  this 
point.  In  the  cortical  sub- 
stance occur  changes  which 
result  in  the  formation  of 
structures  closely  resembling 
the  cortical  nodules  of  lymph- 
glands. 

Until  recently,  little  was 
known  of  the  significance  of  this 
organ.  A  careful  study  re- 
vealed a  similarity  between  cer- 
tain cellular  elements  of  the 
thymus  and  the  constituents  of 
the  blood  -  forming  organs, — 

a  similarity  still  more  striking  from  the  presence  of  nucleated 
red  blood-cells  in  the  thymus.  Logically,  then,  the  embryonal 
thymus  is  to  be  regarded  as  one  of  the  blood-forming  organs 
(Schaffer,  93,  I).  The  meshes  of  the  capillary  network  are 
much  wider  in  the  medullary  than  in  the  cortical  substance  of  the 


fc- 


Fig.  163. — Hassal' s  corpuscle  and  a  small 
portion  of  medullary  substance,  showing 
reticulum  and  cells,  from  thymus  of  a  child 
ten  days  old. 


I9O  THE    CIRCULATORY    SYSTEM. 

lobules,  but  small  arteries  also  penetrate  directly  into  the  cortex. 
The  lymphatics,  concerning  the  origin  of  which  nothing  certain  is 
known,  pass  out  side  by  side  with  the  arteries.  It  is  probable  that 
the  peripheral  looser  portion  of  the  cortex  represents  a  lymph-sinus. 
During  embryonic  life  from  the  fourth  month  on  and  for  some 
time  after  birth,  there  are  found  in  the  thymus  peculiar  epithelial 
bodies,  known  as  the  corpuscles  of  Hassal.  They  are  spheric  struc- 
tures, about  o.  I  mm.  in  diameter,  whose  periphery  shows  a  con- 
centric arrangement  of  the  epithelial  cells.  In  their  central  portions 
are  found  a  few  nuclear  and  cellular  fragments.  These  bodies 
occur  only  in  the  thymus  gland.  They  are  remnants  of  the  primary 
epithelial,  glandular  structure  of  the  thymus,  and  are  formed  by  an 
ingrowth  of  mesoderm  which  breaks  down  the  epithelium  into  small 
irregular  masses,  mechanically  compressed  by  the  proliferating 
mesoderm. 


II.  THE  CIRCULATORY  SYSTEM. 

THE  walls  of  the  blood-vessels  vary  in  structure  in  the  different 
divisions  of  the  vascular  system.  All  the  vessels,  including  the 
heart,  possess  an  inner  endothelial  lining.  In  addition  to  this,  the 
larger  vessels  are  provided  with  other  layers,  which  consist,  on  the 
one  hand,  of  connective  and  elastic  tissue  and,  on  the  other,  of  non- 
striated  muscle-fibers.  The  vessels  are  also  richly  supplied  with 
nerves,  that  form  plexuses  in  which  ganglion  cells  are  sometimes 
found,  and  in  the  larger  vessels  the  outer  layer  is  honeycombed  by 
nutrient  blood-vessels,  called  vasa  vasorum.  In  the  heart,  the  mus- 
cular tissue  is  especially  well  developed.  According  to  the  structure 
of  the  vessels,  we  distinguish,  in  both  arteries  and  veins,  large, 
medium-sized,  small,  and  precapillary  vessels,  and  finally,  the  capil- 
laries themselves.  The  latter  connect  the  arterial  and  venous  pre- 
capillary vessels.  In  the  lymphatic  system  we  must  further  dis- 
tinguish between  the  larger  lymph-vessels,  the  sinuses,  and  the 
capillaries. 

A.  THE  VASCULAR  SYSTEM. 

J,  THE  HEART, 

In  the  heart  there  are  recognized  three  main  coats — the  endo- 
cardium, the  myocardium,  and  the  pericardium  or  epicardium. 

The  endocardium  consists  of  plate-like  endothelial  cells,  with 
very  irregular  outlines.  Beneath  this  endothelial  layer  is  a  thin 
membrane  composed  of  unstriped  muscle-cells,  together  with  a 
small  number  of  connective-tissue  and  elastic  fibers.  Below  this  is 
a  somewhat  thicker  and  looser  layer  of  elastic  tissue  connected  ex- 
ternally with  the  myocardium.  Between  the  two  layers  are  found, 
here  and  there,  traces  of  a  layer  of  Purkinje's  fibers  (compare  p. 


THE    VASCULAR    SYSTEM.  IQI 

132).  Purkinje's  fibers  are  found  in  the  heart  of  many  mammalia, 
although  absent  in  the  heart  of  the  human  adult. 

The  auricnlovctitricular  valves  of  the  heart  represent,  in  general, 
a  duplication  of  the  endocardium.  The  layer  of  smooth  muscle- 
fibers  found  in  the  latter  is  better  developed  on  the  auricular  surface, 
while  the  elastic  tissue  is  not  more  prominent  on  the  ventricular 
surface.  At  the  points  of  insertion  of  the  chordae  tendineae  the  con- 
nective-tissue layer  is  strongly  developed  and  assumes  a  tendon-like 
consistency.  The  scmilunar  valves  of  the  aorta  and  pulmonary 
artery  have  a  similar  structure.  In  the  nodules  of  these  valves  the 
elastic  fibers  are  especially  dense  in  their  arrangement. 

The  myocardium  is  made  up  of  the  heart  muscle-cells  already 
described  (vid.  p  132).  Between  the  heart  muscle-fibers  and  bundles 
of  such  fibers  are  thin  layers  of  fibrous  connective  tissue  containing 
a  network  of  capillaries.  The  myocardium  of  the  auricles  may  be 
divided  into  two  layers,  of  which  the  outer  is  common  to  both 
auricles  ;  the  heart  muscle-fibers  of  this  layer  have  a  nearly  circular 
arrangement.  Three  layers  of  muscle-fibers  are  met  with  in  a 
longitudinal  section  through  the  ventricular  wall,  the  outer  and 
inner  being  chiefly  longitudinal  in  direction,  although  not  exactly 
parallel.  In  the  left  ventricle  the  outer  layer  is  very  strongly  devel- 
oped. The  musculature  of  the  auricles  is  almost  completely  sepa- 
rated from  that  of  the  ventricles  by  means  of  the  anmtlus  fibrosiis 
atrioventricularis ,  which  consists  in  the  adult  of  connective  tissue 
containing  numerous  delicate  and  densely  interwoven  elastic  fibers. 

The  pericardium  consists  of  a  visceral  layer,  the  epicardium,  ad- 
hering closely  to  the  myocardium,  and  a  parietal  layer  (pericardium), 
loosely  surrounding  the  heart  and  continuous  at  the  upper  portion 
of  the  heart  with  the  visceral  layer.  Between  the  two  layers  is  the 
pericardial  cavity,  containing  a  small  quantity  of  a  serous  fluid — 
the  pericardial  fluid.  In  the  visceral  layer  (the  epicardium)  we 
find  a  connective-tissue  stroma  covered  by  flattened  endothelial 
cells.  A  similar  structure  occurs  also  in  the  parietal  layer,  although 
here  the  connective-tissue  stroma  is  considerably  reinforced.  De- 
posits of  fat,  in  most  cases  in  the  neighborhood  of  the  blood-vessels, 
are  sometimes  seen  between  the  myocardium  and  the  visceral  layer 
of  the  pericardium. 

According  to  Seipp,  the  distribution  of  the  elastic  tissue  in  the 
heart  is  as  follows  :  The  endocardium  of  the  ventricles  contains  far 
more  elastic  tissue  than  that  of  the  auricles,  especially  in  the 
left  ventricle,  where  even  fenestrated  membranes  may  be  present. 
In  the  myocardium  of  the  ventricles  there  are  no  elastic  fibers  aside 
from  those  which  are  found  in  the  adventitia  of  the  contained  blood- 
vessels. In  the  myocardium  of  the  auricles,  on  the  contrary,  such 
fibers  are  very  numerous  and  are  continuous  with  the  elastic 
elements  in  the  walls  of  the  great  veins.  The  epicardium  also  pre- 
sents elastic  fibers  in  the  auricles  continuous  with  those  of  the  great 
veins  emptying  into  the  heart,  and  in  the  ventricles  continuous  with 


-THE    CIRCULATORY    SYSTEM. 

those  in  the  adventitia  of  the  conus  arteriosus.  In  those  portions 
of  the  heart-wall  containing  no  muscular  tissue  the  elastic  elements 
of  the  epicardium  are  continuous  with  those  of  the  endocardium.  In 
the  new-born  the  cardiac  valves  possess  no  elastic  fibers,  although 
they  are  present  in  the  adult.  They  are  developed  on  that  side  of 
each  valve,  which,  on  closing,  is  the  more  stretched — for  instance, 
on  the  auricular  side  of  the  auriculoventricular  valves. 

The  heart  has  a  rich  blood  supply.  The  capillaries  of  the  myo- 
cardium are  very  numerous,  and  so  closely  placed  around  the 
muscle  bundles  that  each  muscular  fiber  comes  in  contact  with  one 
or  more  capillaries.  In  the  endocardium  the  vessels  are  confined 
to  the  connective  tissue.  The  auriculoventricular  valves  con- 
tain blood-vessels,  in  contradistinction  to  the  semilunar  valves, 
which  are  non-vascular,  while  the  chordae  tendineae  are  at  best  very 
poorly  supplied  with  capillaries. 

The  coronary  arteries,  which  terminate  in  the  capillaries  above 
mentioned,  are  terminal  arteries  in  the  sense  that  "  the  resistance  in 
the  anastomosing  branches  is  greater  than  the  blood,  pressure  in  the 
arteries  leading  to  those  branches  (Pratt,  98).  This  observer  has 
further  shown  that  the  vessels  of  Thebesius  (small  veins  which 
open  on  the  endocardial  surfaces  of  the  ventricles  and  auricles  and 
communicate  directly  with  all  the  chambers  of  the  heart)  "  open 
from  the  ventricles  and  auricles  into  a  system  of  fine  branches  that 
communicate  with  the  coronary  arteries  and  veins  by  means  of 
capillaries,  and  with  the  veins,  but  not  with  the  arteries,  by  passages 
of  somewhat  larger  size";  so  that,  although  the  blood  supply  through 
the  coronary  arteries  for  a  given  area  of  the  myocardium  is  cut  off, 
the  heart  muscle  of  this  area  may  receive  blood  through  the  vessels 
of  Thebesius. 

Lymphatic  networks  have  been  shown  to  exist  in  the  endocar- 
dium, and  their  presence  in  the  pericardium  is  not  difficult  to  demon- 
strate. Little  is  known  with  regard  to  the  lymph-channels  of  the 
myocardium. 

The  nerve  supply  of  the  heart  includes  numerous  medullated 
nerve-fibers,  the  dendrites  of  sensory  neurones,  and  numerous  non- 
medullated  fibers,  the  neuraxes  of  sympathetic  neurones.  Smirnow 
(95)  described  sensory  nerve -endings  in  the  endocardium  of  amphibia 
and  mammalia,  which  he  suggests  may  be  the  terminations  of  the 
depressor  nerve.  Dogiel  (98)  has  corroborated  and  extended  these 
observations,  and  has  described  complicated  sensory  telodendria 
situated  both  in  the  endo-  and  pericardium.  The  latter  states  that, 
after  forming  plexuses  and  undergoing  repeated  division,  the  medul- 
lated sensory  nerves  lose  their  medullary  sheaths,  the  neuraxes 
further  dividing  in  numerous  varicose  fibers,  variously  interwoven 
and  terminating  in  telodendria,  which  vary  greatly  in  shape  and 
configuration.  These  telodendria  are  surrounded  by  a  granular 
substance  containing  branched  cells,  probably  connective-tissue 
cells,  the  interlacing  branches  of  which  form  a  framework  for  the 


THE    VASCULAR    SYSTEM.  193 

telodendria.  Similar  sensory  nerve-endings  occur  in  the  adventitia 
of  the  arteries  and  veins  of  the  pericardium  (Dogiel,  98)  ;  and 
Schemetkin  has  shown  that  sensory  nerve-endings  occur  in  the  adven- 
titia and  intima,  especially  in  the  latter,  of  the  arch  of  the  aorta  and 
pulmonary  arteries.  In  the  heart,  under  the  pericardium  on  the 
posterior  wall  of  the  auricles  and  in  the  sulcus  coronarius,  are  found 
numerous  sympathetic  neurones  whose  cell -bodies  are  grouped 
to  form  sympathetic  ganglia.  The  neuraxes  of  these  sympathetic 
neurones — varicose,  nonmedullated  nerve-fibers — form  intricate 
plexuses  situated  under  the  pericardium  and,  penetrating  the  myo- 
cardium, surround  the  bundles  of  heart  muscle-fibers.  From  the 
varicose  nerve-fibers  constituting  these  plexuses,  fine  branches  are 
given  off,  which  terminate  on  the  heart  muscle-cells  in  a  manner 
previously  described  (see  p.  149  and  Fig.  127).  The  cell-bodies  of 
the  sympathetic  neurones,  the  neuraxes  of  which  thus  terminate 
on  the  heart  muscle-fibers,  are  surrounded  by  end-baskets,  the 
telodendria  of  small  medullated  nerve-fibers  which  reach  the  heart 
through  the  vagi.  The  slowed  and  otherwise  altered  action  of  the 
heart-muscle,  produced  on  stimulating  directly  or  indirectly  the 
vagus  nerves  is  therefore  due  not  to  a  direct  action  of  these  nerve- 
fibers  on  the  heart  muscle-cells,  but  to  an  altered  functional  activity 
produced  by  vagus  stimuli  in  at  least  some  of  the  sympathetic  neu- 
rones situated  in  the  heart,  the  neuraxes  of  which  convey  the  im- 
pulse to  the  heart  muscle,  The  heart  receives  further  nerve  supply 
through  sympathetic  neurones,  the  cell-bodies  of  which  are  situated 
in  the  inferior  cervical  and  stellate  ganglia,  the  neuraxes  of  which 
enter  the  heart  as  the  augmentor  or  accelerator  nerves  of  the  heart. 
The  mode  of  ending  of  these  nerve-fibers  has  not  as  yet  been  fully 
determined.  It  may  be  suggested  as  quite  probable  that  they  ter- 
minate on  the  dendrites  of  sympathetic  neurones,  the  cell-bodies  of 
which  are  not  inclosed  by  end-baskets  of  nerves  reaching  the  heart 
through  the  vagi,  as  above  described.  It  is  also  possible  that  they 
end  directly  on  the  heart  muscle-cells.  The  cell-bodies  of  the 
sympathetic  neurones,  the  neuraxes  of  which  form  the  augmentor 
nerves,  are  surrounded  by  the  telodendria  of  small  medullated 
fibers,  forming  end-baskets,  which  leave  the  spinal  cord  through  the 
anterior  roots  of  the  upper  dorsal  nerves.  Besides  the  nerves  here 
described,  nonmedullated  nerves  (whether  the  neuraxes  of  sympa- 
thetic neurones,  the  cell-bodies  of  which  are  situated  inside  or  out- 
side of  the  heart  has  not  been  fully  determined),  form  plexuses  in 
the  walls  of  the  coronary  vessels,  terminating,  it  would  seem,  on  the 
muscle-cells  of  the  media  (vasomotor  nerves). 

2.  THE  BLOOD-VESSELS. 

A  cross-section  of  a  blood-vessel   shows   several  coats.     The 
inner  consists  of  flattened  endothelial  cells,  and  is  common  to  all 
vessels.     The  second  varies  greatly  in  thickness,  contains  most  of 
13 


194 


THE    CIRCULATORY    SYSTEM. 


the  contractile  elements  of  the  arterial  wall,  and  is  known  as  the 
media,  or  tunica  media.  Its  elastic  fibers  have  in  general  a  circular 
arrangement  and  are  fused  at  the  inner  and  outer  surfaces  to  form 
fenestrated  membranes,  the  lamina  elastica  interna  and  externa. 
Outside  of  the  media  lies  the  adventitia  or  tunica  externa,  consist- 
ing in  the  arteries  almost  entirely  of  connective  tissue  and  in  the 
veins  principally  of  contractile  elements,  smooth  muscle-fibers. 
Between  the  internal  elastic  membrane  and  the  endothelial  layer  is 
a  fibrous  stratum  which  varies  in  structure  in  the  different  vessels 
of  larger  caliber.  This  is  the  subendothelial  layer,  or  the  inner 
fibrous  layer,  and  forms,  together  with  the  endothelium,  the  intima 


Intima. 


Endothelium  of 
the  intima. 


Media. 


Fenestrated 
elastic    mem- 
brane. 


Outer  layer  of 

adventitia. 
_1 Vasa  vasorum. 


Fig.  164. — Cross-section  of  the  human  carotid  artery  ;    X  I5°- 


or  tunica  intima.  Bonnet  (96),  as  a  result  of  his  own  investigations, 
suggests  a  somewhat  different  classification  of  the  layers  composing 
the  arterial  wall.  According  to  him,  the  endothelium  alone  con- 
stitutes the  intima.  The  elastic  membranes,  both  internal  and 
external,  together  with  the  tissue  lying  between  them,  and  that 
between  the  internal  elastic  membrane  and  the  intima,  constitute 
the  media.  The  tissue  layers  outside  the  external  elastic  membrane 
form  the  tunica  externa  (adventitia). 

(a)  Arteries. — In  the  great  arterial  trunks,  such  as  the  pulmo- 
nalis,  carotis,  iliaca,  etc.,  the  tunica  media  possesses  a  very  typical 
structure.  It  is  divided  by  means  of  elastic  fibers  and  membranes 


THE    VASCULAR    SYSTEM 


195 


(fenestrated  membranes)  into  a  large  number  of  concentric  layers 
containing  but  few  muscle-fibers.  Here  also  the  tunica  media  is 
separated  from  the  intima  by  an  elastic  limiting  membrane,  the 
fenestrated  membrane  of  Henle,  or  the  lamina  elastica  interna.  In 
the  aorta  this  membrane  as  such  is  not  recognizable.  The  intima 
presents  three  distinct  layers — the  inner  composed  of  flattened  endo- 
thelial  cells,  and  the  other  two  consisting  chiefly  of  elastic  tissue 
(fibrous  layers).  Of  these  latter  the  inner  is  the  richer  in  cellular 


Endothelium  of  the 
"      intima. 
"••  Intima. 

Media. 


Adventitia  with 
nonstriated    mus- 
cle-fibers in  cross- 
section. 


Fig.  165. — Section  through  human  artery,  one  of  the  smaller  of  the  medium-sized  ;  X  640. 

elements  and  has  a  longitudinal  arrangement  of  its  fibers,  while  the 
outer  is  the  looser  in  structure,  possesses  few  cellular  elements,  and 
shows  a  circular  arrangement  of  its  fibers.  The  adventitia  is  also 
made  up  of  fibro-elastic  tissue,  but  in  this  case  with  a  still  looser 
structure  and  a  longitudinal  arrangement  of  its  elastic  fibers.  In  the 
outer  portion  of  the  adventitia  the  white  fibrous  tissue  is  more 
abundant.  The  adventitia  is  rich  in  blood-vessels. 

The  medium-sized  arteries  differ  in  structure  from  the  larger  in 
that  the  elastic  elements  of  the 
intima  and  media  are  replaced  to 
a  considerable  extent  by  nonstri- 
ated muscular  fibers.  To  this  type 
belong  the  majority  of  the  arterial 
vessels,  ranging  in  caliber  from  the 
brachial,  crural,  and  radial  arteries 
to  the  supraorbital  artery.  In 
these  the  intima  shows,  besides  its 
endothelium,  only  a  single  connec- 
tive-tissue layer  with  numerous 
longitudinal  fibers,  the  subendo- 
thelial  layer,  which  is  thin  and  is 
limited  externally  by  the  fenes- 
trated membrane  of  Henle  (lamina 
elastica  interna).  The  media  no  longer  gives  the  impression  of 
being  laminated,  but  consists  of  circularly  arranged  muscle-fibers 
separated  from  each  other  by  elastic  fibers  and  membranes  and  a 
small  amount  of  fibrous  connective  tissue  in  such  a  way  that  the 
muscle-cells  form  more  or  less  clearly  defined  groups.  Here  also 


Fig.  166. — Precapillary  vessels  from 
mesentery  of  cat :  a,  Precapillary  artery  ; 
6,  precapillary  vein  possessing  no  muscu- 
lar tissue. 


196 


THE    CIRCULATORY    SYSTEM. 


the  media  is  limited  externally  by  the  external  elastic  membrane. 
The  adventitia,  which  becomes  looser  externally,  is  not  so  well  de- 
veloped as  in  the  larger  vessels,  but  presents  in  general  the  same 
structure.  In  certain  arteries  (renal,  splenic,  dorsalis  penis)  it  shows 
in  its  inner  layers  scattered  longitudinal  muscle-cells,  which,  how- 
ever, may  also  occur  in  other  arteries  at  their  points  of  division. 

With  regard  to  the  elastic  tissues,  the  arteries  of  the  brain  differ 
to  some  extent  from  those  of  the  remainder  of  the  body.  The 
elastica  interna  is  much  more  prominent,  the  elastic  fibers  in  the 


Elastica  interna. 


Media. 


Fenestrated  elastic 
membrane. 


Blood-    - 
vessel.   I 


Inner  layer  of  the 
adventitia  with 
-    longitudinally  ar- 
ranged muscle- 
cells. 


Connective  tissue 
of  the  adventitia. 


•Nerve. 


Fig.  167. — Cross-section  of  human  internal  jugular  vein.     At  the  left  of  the  nerve  are 
two  large  blood-vessels  with  a  smaller  one  between  them  (vasa  vasorum)  ;   X  I5°- 


circular  muscular  layer  are  few:r,  and  the  longitudinal  strands  are 
almost  entirely  lacking  (H.  Triepel). 

The  walls  of  the  smaller  arteries  consist  mainly  of  the  circular 
muscular  layer  of  the  media.  The  intima  is  reduced  to  the  endo- 
thelium,  which  rests  directly  on  the  elastic  internal  limiting  mem- 
brane. Outside  of  the  external  limiting  membrane  is  the  adventitia, 
which  now  consists  of  a  small  quantity  of  connective  tissue.  The 
vasa  vasorum  have  disappeared.  To  this  type  belong  the  supra- 
orbital,  central  artery  of  the  retina,  etc. 

In  the  so-called  precapillary  vessels  the   intima   consists  only 


THE    VASCULAR    SYSTEM. 


197 


of  the  endothelial  layer.  The  internal  elastic  membrane  is  very 
delicate.  The  media  no  longer  forms  a  continuous  layer,  but  is 
made  up  of  a  few  circularly  disposed  muscular  fibers.  The  adven- 
titia  is  composed  of  a  small  quantity  of  connective  tissue,  and  con- 
tains no  vasa  vasorum. 

(ft)  Veins. — In  the  foregoing  account  of  the  structure  of  the 
arteries  we  have  described  the  structure  of  their  walls  according  to 
the  caliber  of  the  vessels.  Such  a  differentiation  in  the  case  of  the 
veins  would  be  impossible,  since  sometimes  veins  of  the  same  cali- 
ber present  decided  differences  in  structure  in  various  parts  of  the 
body. 

For  the  sake  of  convenience,  we  will   commence  with   the  de- 
scription  of  a   vein  of  medium  size.      Its   intima  consists  of  three 
layers:  (i)   Of  an  inner  layer  of  endothelium  ;  (2)  of  an  underly- 
ing layer  of  muscle-cells,  interrupted  here  and  there  by  connective 
tissue  ;  and  (3)  of  a  fibrous  connective -tissue  layer  containing  fewer 
elastic  but  more  white  fibrous  connective -tissue  fibers  than  is  the 
case  in  the  arteries.      Externally,  the   intima   is  limited  by  an  in- 
ternal elastic   layer.      The 
media    is    in    general    less 
highly  developed  than  that 
of  a  corresponding  artery, 
and    contains    muscle-cells 
which    have  a  circular  ar- 
rangement    and     in     some 
veins    form     a    continuous 
layer,  although  they  some- 
times occur  as  isolated  fi- 
bers.   The  adventitia  shows 

an  inner  longitudinal  muscular  layer,  which  may  be  quite  promi- 
nent and  even  form  the  bulk  of  the  muscular  tissue  in  the  wall  of 
the  vein.  Otherwise  the  adventitia  of  the  veins  belonging  to  this 
class  corresponds  in  general  to  that  of  the  arteries  of  the  same 
size ;  but  here  also  we  have,  as  in  the  intima,  a  preponderance  of 
white  fibrous  connective-tissue  elements. 

In  the  crural,  brachial,  and  subcutaneous  veins,  the  muscula- 
ture of  the  media  is  prominent ;  while  in  the  jugular,  subclavian, 
and  innominate  veins,  and  in  those  of  the  dura  and  pia  mater,  the 
muscular  tissue  of  the  media  is  entirely  wanting,  and,  as  a  conse- 
quence, the  adventitia  with  its  musculature,  if  present,  is  joined 
directly  to  the  intima. 

In  the  smaller  veins  the  vascular  wall  is  reduced  to  an  endothe- 
lial lining,  an  internal  elastic  membrane,  a  media  consisting  of 
interrupted  circular  bands  of  smooth  muscle-fibers  (which  may  be 
absent),  and  an  adventitia  containing  a  few  muscle-fibers.  The 
precapillary  veins,  which  possess  in  general  thinner  walls  than  the 
corresponding  arteries,  present  a  greatly  reduced  intima  and  ad- 
ventitia, while  the  media  has  completely  disappeared. 


Intima. 


Media. 


Adventitia  with 
nonstriated 
muscle-cells 
in  cross-sec- 
tion. 


Fig.  1 68. — Section  of  small  vein  (human ] 


IQ8  THE    CIRCULATORY    SYSTEM. 

The  valves  of  the  veins  are  reduplications  of  the  intima  and 
vary  slightly  in  structure  at  their  two  surfaces.  The  inner  surface 
next  to  the  blood  current  is  covered  by  elongated  endothelial  cells, 
while  the  outer  surface  possesses  an  endothelial  lining  composed  of 
much  shorter  cellular  elements.  The  greater  part  of  the  valvular 
structure  consists  of  white  fibrous  connective-tissue  and  elastic  fibers. 
Flattened  and  circularly  arranged  muscle-cells  are  met  with  at  the 
inner  surface  of  many  of  the  larger  valves.  The  elastic  fibers  are 
more  numerous  beneath  the  endothelium  on  the  inner  surface  of  the 
valves  (Ranvier,  89). 

(c)  The  Capillaries. — The  capillaries  consist  solely  of  a  layer  of 
endothelial  cells,  accompanied  here  and  there  by  a  very  delicate  struc- 
tureless membrane,  and  rarely  by  stellate  connective-tissue  cells.  The 
connective  tissue  in  the  immediate  neighborhood  of  the  capillaries 
is  modified  to  such  an  extent  that  its  elements,  especially  those  of  a 
cellular  nature,  seem  to  be  arranged  in  a  direction  parallel  with  the 


Fig.  169.— Endothelial  cells  of  capillary  (a)  and  precapillary  (b)  from  the  mesentery  of 
rabbit ;  stained  in  silver  nitrate. 

long  axis  of  the  capillaries.  When  examined  in  suitable  prepara- 
tions, the  endothelium  of  the  capillaries  is  seen  to  form  a  continuous 
layer,  the  cells  of  which  are,  as  a  rule,  greatly  flattened  and  present 
very  irregular  outlines. 

It  is  a  well-known  fact  that  a  migration  of  the  leucocytes  occurs 
from  the  capillaries  and  smaller  vessels  (compare  p.  175).  In  this 
connection  arises  the  question  as  to  whether  or  not  the  cells  pass 
through  certain  preformed  openings  in  the  endothelium  of  these 
vessels,  the  so-called  stomata,  or  through  the  stigmata  and  intercel- 
lular cement  uniting  the  endothelial  cells.  The  latter  seems  more 
probable,  as  stomata  do  not  occur  normally  in  the  capillary  wall. 
This  subject  will  be  further  touched  upon  in  the  description  of  the 
lymphatic  system. 

The  capillaries  connect  the  arterial  and  venous  precapillary  ves- 
sels, and  in  general  accommodate  themselves  to  the  shape  of  the 
elements  of  tissues  or  organs  in  which  they  are  situated.  In  the 


THE    VASCULAR    SYSTEM. 


199 


muscles  and  nerves,  etc.,  they  form  a  network  with  oblong  meshes, 
while  in  structures  having  a  considerable  surface,  such  as  the  pul- 
monary alveoli,  the  meshes  are  more  inclined  to  be  round  or  oval ; 
such  small  evaginations  of  tissue  as  the  papillae  of  the  skin  contain 
capillaries  arranged  in  the  shape  of  loops.  In  certain  organs — as,  for 
instance,  in  the  lobules  of  the  liver — the  capillaries  form  a  distinct 
network  with  small  meshes. 

(d)  Anastomoses,  Retia  mirabilia,  and  Sinuses. — In  the 
course  of  certain  vessels,  abrupt  changes  are  seen  to  occur — as,  for 
instance,  when  a  small  vessel  suddenly  breaks  up  into  a  network 
of  capillary  or  precapillary  vessels,  which,  after  continuing  as  such 
for  a  short  distance,  again  unite  to  form  a  larger  blood-channel, 
the  latter  then  dividing  as  usual  into  true  capillaries.  Such  struc- 
tures are  known  as  retia  mirabilia,  and  occur  in  man  in  the  kid- 

Sensory  nerve-ending. 

Plexus  of  vasomotor  nerves. 


Fig.    170. — Small  artery  from  the  oral  submucosa   of  cat,   stained  in   methylene- 
blue,  and  showing  a  small  portion  of  a  sensory  nerve-ending  and  the  plexus  of  vasomotor 


ney,  .intestine,  etc.  Again,  instead  of  breaking  up  into  capillaries, 
a  vessel  may  empty  into  a  large  cavity  lined  by  endothelial  cells 
(blood  sinus).  The  latter  is  usually  surrounded  by  loose  con- 
nective tissue  and  is  capable  of  great  distention  when  filled  with 
blood  from  an  afferent  vessel,  or  when  the  lumen  of  the  efferent 
vessel  is  contracted  by  pressure  or  otherwise.  The  cavernous  or 
erectile  tissue  of  certain  organs  is  due  to  the  presence  of  such 
sinuses  (penis,  nasal  mucous  membrane,  etc.).  If  vessels  of  larger 
caliber  possess  numerous  direct  communications,  a  vascular  plexus 
is  the  result  ;  but  if  such  communications  occur  at  only  a  few 
points,  we  speak  of  anastomoses.  Especially  important  are  the 
direct  communications  between  arteries  and  veins  without  the 
mediation  of  capillaries.  Certain  structural  conditions  of  the  tis- 
sue appear  to  favor  such  anomalies,  which  occur  in  certain  exposed 


200  THE    CIRCULATORY   SYSTEM. 

areas  of  the  skin  (ear,  tip  of  nose,  toes)  and  in  the  meninges,  kid- 
ney, etc. 

The  blood-vessels,  and  more  particularly  the  arteries,  possess  a 
rich  nerve  supply,  comprising  both  nonmedullated  and  medullated 
nerves.  The  nonmedullated  nerves,  the  neuraxes  of  sympathetic 
neurones,  the  cell-bodies  of  which  are  situated  as  a  very  general 
rule  in  some  distant  ganglion,  form  plexuses  in  the  adventitia  of  the 
vessel-walls  ;  from  this,  single  nerve-fibers,  or  small  bundles  of  such, 
are  given  off,  which  enter  the  media  and,  after  repeated  division, 
end  on  the  involuntary  muscle-cells  in  a  manner  previously  de- 
scribed. (See  p.  149  and  Fig.  128.)  Through  the  agency  of  these 
nerves,  the  caliber  of  the  vessel  is  controlled.  They  are  known  as 
vasomotor  nerves.  Quite  recently  Dogiel,  Schemetkin,  and  Huber 
have  shown  that  many  vessels  possess  also  sensory  nerve-endings. 
The  medullated  nerve-fibers  terminating  in  such  endings,  branch 
repeatedly  before  losing  their  medullary  sheaths.  These  nerve-fibers 
with  their  branches  accompany  the  vessels  in  the  fibrous  tissue 
immediately  surrounding  the  adventitia.  The  nonmedullated  ter- 
minal branches  end  in  telodendria,  consisting  of  small  fibrils,  beset 
with  large  varicosities  and  usually  terminating  in  relatively  large 
nodules. 

The  branches  and  telodendria  of  a  single  medullated  nerve-fiber 
(sensory  nerve)  terminating  in  a  vessel  are  often  spread  over  a 
relatively  large  area,  some  of  the  branches  of  such  a  nerve  often 
accompanying  an  arterial  branch,  to  terminate  thereon.  In  the 
large  vessels,  the  telodendria  of  the  sensory  nerves  are  found  not 
only  in  the  adventitia,  but  also  in  the  intima,  as  has  been  shown  by 
Schemetkin.  (See  p.  193.) 


B.  THE  LYMPHATIC  SYSTEM. 

J.  LYMPH-VESSELS. 

The  larger  lymph-vessels — the  thoracic  duct,  the  lymphatic 
trunks,  and  the  lymph-vessels — have  relatively  thin  walls,  and 
their  structure  corresponds  in  general  to  that  of  the  veins.  They 
possess  numerous  valves,  and  are  subject  to  great  variation  in  cali- 
ber according  to  the  amount  of  their  contents.  When  empty,  they 
collapse  and  the  smaller  ones  are  not  easily  distinguished  from  the 
surrounding  connective  tissue.  Timofeew  and  Dogiel  (97)  ha^e 
shown  that  the  lymph -vessels  are  supplied  with  nerves,  which  in 
their  arrangement  are  similar  to  those  found  in  the  arteries  and 
veins,  though  not  so  numerous.  The  latter,  who  has  given  the 
fuller  description,  states  that  the  nerves  supplying  the  lymph- 
vessels  are  varicose,  nonmedullated  fibers  which  form  plexuses  sur- 
rounding these  structures.  The  terminal  branches  would  appear 
to  end  on  the  nonstriated  muscle  cells  found  in  the  wall  of  the 
lymph-vessel. 


THE    LYMPHATIC    SYSTEM.  2OI 

2.  LYMPH  CAPILLARIES,  LYMPH-SPACES,  AND  SEROUS  CAVITIES. 

The  walls  of  the  lymph  capillaries  consist  of  very  delicate,  flat- 
tened endothelial  cells,  which  are,  however;  somewhat  larger  and 
more  irregular  in  outline  than  those  of  the  vascular  capillaries.  The 
two  may  also  be  further  differentiated  by  the  fact  that  the  diameter 
of  the  lymph  capillaries  varies  greatly  within  very  short  distances. 
From  a  morphologic  standpoint,  the  relations  of  the  lymph  capil- 
laries to  the  vascular  capillaries  and  adjacent  tissues  are  among  the 
most  difficult  to  solve.  The  distribution  of  the  lymph-vessels  and 
capillaries  can  be  studied  only  in  injected  preparations,  and  it  is 
easily  seen  that  structures  of  such  elasticity  and  delicacy  are  pecu- 
liarly liable  to  injury  by  bursting  under  this  method  of  treatment. 
The  resulting  extravasations  of  the  injection-mass  then  spread  out 
in  the  direction  of  least  resistance  and  still  further  obscure  the 
picture,  rendering  it  difficult  to  determine  what  spaces  are  preformed 
and  what  are  the  result  of  the  injection.  So  much  is,  however,  cer- 
tain :  that  the  more  carefully  and  skilfully  the  injection  is  made,  the 
greater  are  the  areas  obtained,  showing  the  injection  of  true  lymph 
capillaries. 

In  some  regions  very  dense  networks  of  lymph  capillaries  sur- 
rounding the  smaller  blood-vessels  have  been  demonstrated.  Larger 
cleft-like  spaces,  lined  with  endothelium  and  communicating  with 
the  lymphatic  system,  are  also  found  surrounding  the  vessels,  peri- 
vascular  spaces.  These  are  present  in  man  in  the  Haversian  canals 
of  bone  tissue,  around  the  vessels  of  the  central  nervous  system, 
etc.,  and  are  separated  from  the  actual  vessel-wall  by  flattened  endo- 
thelial cells.  As  in  the  case  of  the  so-called  perilympJiatic  spaces, 
the  walls  of  the  perivascular  spaces  are  joined  here  and  there  by 
connective-tissue  trabecula:;  covered  by  endothelium.  Such  struc- 
tures exist  in  the  perilymphatic  spaces  of  the  ear,  the  subdural 
spaces  of  the  pia,  the  subarachnoidal  space,  the  lymph-sinuses,  etc. 
The  perivascular  spaces  are  better  developed  in  the  lower  animals 
(amphibia,  Teptilia,  etc.)  than  in  mammalia. 

The  cell-spaces,  with  their  anastomosing  processes,  found  in  con- 
nective tissue  and  previously  described  as  the  lymph-canalicular 
system,  possess  no  endothelial  lining  and  communicate  directly  or 
indirectly  with  the  lymph  capillaries.  To  the  lymphatic  system 
belong  also  the  body-cavities,  the  pleural,  pericardial,  and  peritoneal 
cavities.  The  walls  of  these  consist  of  a  connective-tissue  stroma 
rich  in  lymph-spaces,  lymph  capillaries  and  lymph-vessels,  and  are 
lined  by  a  layer  of  mesothelial  cells.  In  them  are  found  the  stig- 
mata and  stomata  mentioned  in  a  former  section.  (See  p.  85.) 
The  synovial  spaces  belong  also  to  the  lymphatic  system  ;  they  are 
lined  by  a  layer  of  endothelial  cells. 

Mention  has  been  made  of  the  migration  of  leucocytes  and, 
under  certain  conditions,  of  red  blood-cells  through  the  walls  of 
blood  capillaries,  and  in  the  case  of  the  former  through  the  walls  of 


2O2  THE    CIRCULATORY    SYSTEM. 

lymph  capillaries  and  lymph-vessels  and  spaces.  This  diapedesis  of 
leucocytes  probably  takes  place  by  a  wandering  of  these  cells 
through  the  stigmata  and  intercellular  cement  uniting  the  endo- 
thelial  cells  lining  these  spaces,  and  through  the  stomata  in  regions 
where  these  occur.  According  to  later  investigations,  it  would 
seem  that  leucocytes  may  bore  through  endothelial  cells,  and  thus 
migrate  from  the  vessel  or  space  in  which  they  are  found  previous 
to  such  migration.  Kolossow  (93),  as  a  result  of  his  investigations, 
advances  still  another  theory.  He  believes  that  he  has  demonstrated 
that  the  cells  lining  the  body-cavities  are  joined  to  each  other  by 
protoplasmic  processes,  and  that  their  inner  surfaces  are  covered  by 
a  cuticular  membrane.  These  structures  are  especially  well  seen  in 
the  serous  membranes  of  certain  reptiles.  Between  the  cells  and 
between  the  protoplasmic  processes  connecting  them  are  spaces 
which  may  be  compared  to  the  intercellular  spaces  found  in  the 
epidermis.  It  is  thought  by  him  that  on  stretching  the  serous 
membranes,  the  spaces  between  the  lining  cells  become  larger,  and 
the  cuticular  portions  of  the  cells  become  separated  from  each  other, 
and  in  this  way  the  stomata  and  stigmata  are  thought  to  be  tem- 
porarily formed,  and  through  these  the  migration  of  the  leucocytes 
is  believed  to  occur.  This  process  is  also  supposed  to  occur  in  the 
smaller  vessels  and  in  the  vascular  and  lymphatic  capillaries.  How- 
ever, this  whole  question  needs  further  investigation. 


C  THE  CAROTID  GLAND   (GLANDULA  CAROTICA, 
GLOMUS  CAROTICUM). 

At  the  point  where  the  common  carotid  divides,  there  lies  in 
man  a  small  oval  structure  about  the  size  of  a  grain  of  wheat,  known 
as  the  carotid  gland  or  the  glomus  caroticum.  It  is  imbedded  in 
connective  tissue,  surrounded  by  many  nerve-fibers,  and  on  account 
of  its  great  vascularity  has  a  decidedly  red  color.  The  connective- 
tissue  envelope  pf  the  gland  penetrates  into  the  interior  in  the  form 
of  septa,  which  divide  its  substance  into  small  lobules,  and  these  in 
turn  into  smaller  round  masses,  the  cell-balls.  A  small  branch 
from  the  internal  or  external  carotid  enters  the  gland,  where 
it  branches,  sending  ofT  twigs  to  the  lobules,  and  these  in  turn  still 
smaller  divisions  to  the  cell-balls.  The  latter  vessels  break  up  into 
capillaries,  which  merge  at  the  periphery  of  each  cell-ball  to  form  a 
small  vein,  from  which  the  larger  trunks  that  pass  from  the  lobules 
are  derived.  Each  lobule  is  thus  surrounded  by  a  venous  plexus 
from  which  the  larger  veins  originate  that  leave  the  organ  at  sev- 
eral points.  The  cell-balls  are  composed  of  cellular  cords,  or 
trabeculae,  the  elements  of  which  are  extremely  sensitive  to  the 
action  of  reagents.  The  cells  are  round  or  irregularly  polygonal 
and  separated  from  each  other  by  a  scanty  reticular  connective 
tissue.  The  capillaries  already  mentioned  come  in  direct  contact 


THE    CAROTID   GLAND. 


203 


with  the  cells  of  the  cell-balls.     The  organ  contains  a  relatively 
large  number  of  nerve-fibers  and  a  few  ganglion  cells. 

As  the  individual  grows  older,  the  organ  undergoes  changes 
which  finally  make  it  unrecognizable.  The  former  belief  that  the 
carotid  gland  was  developed  as  an  evagination  of  one  of  the  visceral 
pouches  has  been  replaced  by  a  newer  theory  which  gives  it  an 
origin  solely  from  the  vessel-wall  (vid.  Schaper).  The  structure  of 
the  coccygeal  gland  is  in  general  like  that  of  the  carotid  gland 
here  described. 


Septum. 


Trabecula  of 
cells  in  cross- 
section. 

Distended 
blood  capil- 
laries. 


ii._"l    ..   Efferent  vein. 


Fig.  171. — Section  of  a  cell-ball  from  the  glomus  caroticum  of  man  ;   X  I^°-      (Injected 
specimen,  after  Schaper.) 


TECHNIC   (BLOOD  AND  BLOOD-FORMING  ORGANS). 

184.  Red  blood-corpuscles  may  be  examined  in  the  blood  fluid  without 
special  preparation.  The  tip  of  the  finger  is  punctured  and  a  small  drop 
of  blood  pressed  out,  placed  upon  a  slide,  and  immediately  covered 
with  a  cover-glass  and  examined.  In  such  preparations  the  red  blood- 
cells  soon  become  crenated.  The  evaporation  causing  the  crenation  may 
be  prevented  by  surrounding  the  cover-glass  with  oil  (olive  oil).  A  fluid 
having  but  a  slight  effect  upon  the  red  blood-cells  is  Hay  em's  solution, 
which,  however,  is  not  adapted  to  the  examination  of  leucocytes.  It 
consists  of  sodium  chlorid  i  gm.,  sulphate  of  soda  5  gm.,  corrosive  subli- 
mate 0.5  gm.,  and  water  200  gm.  The  fresh  blood  is  brought  directly 
into  this  solution,  the  amount  of  which  should  be  at  least  one  hundred 
times  the  volume  of  the  blood  to  be  examined.  The  fixed  blood-cells 
sink  to  the  bottom,  and  after  twenty-four  hours  the  fluid  is  carefully 
poured  off  and  replaced  by  water.  The  blood-corpuscles  are  then 
removed  with  a  pipet  and  examined  in  dilute  glycerin.  They  may  be 
stained  with  eosin  and  hematoxylin. 


2O4  THE    CIRCULATORY    SYSTEM. 

185.  Fresh  red  blood-corpuscles  may  also  be  fixed  in  osmic  acid  and 
other  special  fixing  agents.     This  is  done  by  dropping  a  small  quantity  of 
blood  into  the  fixing  fluid  ;    the  blood-cells  immediately  sink  and  allow 
the  osmic  acid  to  be  decanted  ;    they  are  then  washed  with  water,  drawn 
up  with  a  pipet,  and  examined  in  dilute  glycerin. 

1 86.  A  method  almost  universally  used   consists  in  preserving  the 
blood-corpuscles  in  dry  preparations.     A  drop  of  fresh  blood  is  placed 
between  two  thoroughly  cleaned  cover-glasses,  which  are  then  quickly 
drawn  apart,  leaving  on  the  surface  of  each  a  thin  film  of  blood  which 
dries  in  a  few  moments  at  ordinary  room  temperature.     The  specimens 
are  further  dried  for  several  hours  at  a  temperature  of  i2o°C.     After 
they  have  been  subjected  to  this  process,  they  may  be  stained,  etc. 

187.  The  same  results  may  be  obtained  by  treating  specimens  dried 
in  the  air  with  a  solution  of  equal  parts  of  alcohol  and  ether  for  from  one 
to  twenty-four  hours,  after  which  they  are  again  dried  in  the  air,  and  are 
then  ready  for  further  treatment. 

188.  A  cover-glass  preparation  of  fresh  blood  may  also  be  treated  for  a 
quarter  of  an  hour  with  a  concentrated  solution  of  corrosive  sublimate  in 
saline  solution,  then  washed  with  water,  stained,  dehydrated  with  alcohol 
and  mounted  in  Canada  balsam.     A  concentrated  aqueous  solution  of 
picric  acid  may  also  be  used,  but  in  this  case  the  specimen  should  remain 
in  it  for  from  twelve  to  twenty -four  hours. 

189.  The  elements  of  the  blood  may  also  be  examined  in  sections. 
Small  vessels  are  ligated  at  both  ends,  removed,  fixed  with  osmic  acid, 
corrosive  sublimate,  or  picric  acid,  and  imbedded  in  paraffin. 

190.  After  fixation  by  any  of  the  above  methods  the  blood-cells  may 
be  stained.      Eosin  brings  out  very  well  the  hemoglobin  in  the  blood- 
cells,  coloring  it  a  brilliant  red ;  the  stain  should  be  used  in  very  dilute 
aqueous  or  alcoholic  solutions  (i%  or  less),  or  in  combination  with  alum 
(eosin  i  gm.,  alum  i  gm.,  and  absolute  alcohol  200  c.c.,  E.  Fischer). 
Eosin  may  also  be  used  as  a  counterstain  subsequent  to  a  nuclear  stain — 
for  instance,  hematoxylin.     The  preparation  is  stained  for  about  ten  min- 
utes, then  washed  in  water  or  placed  in  alcohol  until  the  blood-cells  alone 
remain  colored ;    the  cover-glass  preparation  should  then  be  thoroughly 
dried   between  filter-paper  and  mounted   in   Canada  balsam.       Besides 
eosin,  other  acid  stains — as  orange  G,  indulin,  and  nigrosin — have  the 
property  of  coloring  blood-cells  containing  hemoglobin. 

191.  Blood  platelets  are  best  fixed  with  osmic  acid,  and  may  be  seen 
without  staining.     They  may  also  be  stained  and  preserved  in  a  sodium 
chlorid    solution   to  which  methyl -violet   is  added  in  a  proportion  of 
i  :  20000   (Bizzozero,  82).     Afanassiew  adds  0.6%   of  dry  peptone  to 
the  solution  (this  fluid  must  be  sterilized  before  using). 

192.  The  leucocytes  of  the    circulating   blood   and  those  found  in 
certain  organs  possess  granulations  which  were  first  studied  by  Ehrlich 
and  his  pupils,  and  which  may  be   demonstrated  by  certain  methods. 
The  names  given  to  these  granulations  are  based  upon  Ehrlich's  classifica- 
tion of  the  anilin  stains,  which  differs  from  that  of  the  chemist.     This 
author  distinguishes  acid,  basic,  and  neutral  stains.     By  the  acid  stains  he 
understands  those  combinations  in  which  the  acid  is  the  active  staining 
principle,  as  in  the  case  of  the  picrate  of  ammonia.     Among  these  are 
congo,   eosin,   orange   G,  indulin,  and  nigrosin.     The  basic  stains  are 


TECHNIC  (BLOOD  AND  BLOOD-FORMING  ORGANS).  205 

those  which,  like  the  acetate  of  rosanilin,  consist  of  a  color  base  and  an 
indifferent  acid.  To  these  belong  fuchsin,  Bismarck  brown,  safranin, 
gentian,  dahlia,  methyl-violet,  methylene-blue,  and  toluidin.  Finally, 
the  neutral  anilins  may  be  considered  as  those  stains  which,  like  the  pic- 
rate  of  rosanilin,  are  formed  by  the  union  of  a  color  base  with  a  color 
acid.  The  granula  may  be  demonstrated  in  dry  preparations  as  well  as 
in  those  fixed  with  alcohol,  corrosive  sublimate,  glacial  acetic  acid,  and 
sometimes  even  Flamming' s  solution.  Five  kinds  of  granules  are  distin- 
guished, and  designated  by  the  Greek  letters  from  alpha  to  epsilon. 

193.  The  a-granules  (acidophile,  eosinophile)  occur  in  leucocytes 
of  the  normal  blood,  in  the  lymph,  and  in  the  tissues,  and  are  differen- 
tiated from  the  others  by  their  peculiar  staining  reaction  to  all  acid  stains. 
They  are  first  treated  for  some  hours  with  a  saturated  solution  of  an  acid 
stain  (preferably  eosin)  in  glycerin,  washed  with  water,  subsequently  col- 
ored with  a  nuclear  stain  (as  hernatoxylin  or  methylene-blue),  and  then 
dried  and  mounted  in  Canada  balsam.      Sections  may  be  treated  in  the 
same  way,  with  the  exception  that  after  being  washed  with  water,  they 
are  first  dehydrated  with  absolute  alcohol  before  mounting  in  balsam. 

194.  Another  method  by  which  both  nuclei  and  granules  are  stained 
consists  in  the  use  of  Ehrlich's  hernatoxylin  solution   (irid.  T.  63,  page 
42),   to  which  0.5%  eosin  is  added.      Before  using,  the  solution  should 
be  permitted  to  stand  exposed  to  the  light  for  three  weeks.     This  mixture 
stains  in  a  few  hours,  after  which  the  preparation  is  washed  with  water, 
treated   with  alcohol,   and    then    mounted    in    Canada    balsam.     The 
a-granules  appear  red,  the  nuclei  blue. 

195.  The  /9-granules  (amphophile,  indulinophile)  stain  as  well  in 
acid  as  in  basic  anilins.     They  do  not  occur  in  man,  but  may  be  observed 
in  the  blood  of  guinea-pigs,  fowl,  rabbits,  etc.^   They  are  demonstrated 
as  follows  :      Equal  parts  of  saturated  glycerin  solutions  of  eosin,   naph- 
thylamin -yellow,  and  indulin  are  mixed,  and  the  dried  preparations  treated 
with  this  combination  for  a  few  hours,  then  washed  with  water,  dried 
between  filter-paper,  and  mounted  in  Canada  balsam.     The  amphophile 
granules  are  stained  black,  the  eosinophile  granules  red,  the  nuclei  black, 
and  the  hemoglobin  yellow. 

196.  The  ^-granules,  or  those  of  the  mast-cells,  are  found  in  normal 
tissues  and  also  in  small  quantities  in  normal  blood,  and  are  found  in 
larger  numbers  in  leukemic  blood.    They  may  be  shown  by  two  methods  : 
( i )  A  mixture  is  made  consisting  of  concentrated  solution  of  dahlia  in 
glacial  acetic  acid  12.5  c.c.,  absolute  alcohol  50  c.c.,  distilled  water  100 
c.c.  (Ehrlich).     The  treatment  is  the  same  as  for  the  amphophile  gran- 
ules ;   (2)   Westphal's  alum-carmin-dahlia  solution  (vid.  Ehrlich).     This 
mixture  is  used  in  staining  dry  preparations  as  well  as  sections  of  objects 
fixed  for  at  least  one  week  in  alcohol.      Alum  i  gm.  is  dissolved  in  dis- 
tilled water  100  c.c.,  and  carmin    i   gm.   added.     The  whole  is  then 
boiled  for  one-quarter  hour,  cooled,  filtered,  and  0.5   c.c.   of  carbolic 
acid  added    (Grenacher's  alum -carmin,   vid.   T.  60).      This  solution  is 
now  mixed  with   100  c.c.  of  a  saturated  solution  of  dahlia  in  absolute 
alcohol,  glycerin  50  c.c.,  and  glacial  acetic  acid  10  c.c.,  the  whole  stirred 
and  allowed  to  stand  for  a  time.     The  specimen  is  stained  for  twenty-four 
hours,  decolorized  in  absolute  alcohol  for  the  same  length  of  time,  and 
finally  mounted  in  Canada  balsam.     The  ^-granules  are  colored  a  dark 
blue   and    the    nuclei    red.     A   simpler   method    of   demonstrating   the 


2O6  THE    CIRCULATORY    SYSTEM. 

^-granules  consists  in  overstaining  dry  and  fixed  cover-glass  preparations 
with  a  saturated  aqueous  solution  of  methylene-blue,  decolorizing  for  some 
time  in  absolute  alcohol,  drying  between  filter-papers,  and  mounting  in 
Canada  balsam. 

197.  The  ^-granules  (basophile)  occur  in  mononuclear  leucocytes 
of  the  human  blood.     Their  staining  may  be  accomplished  in  a  few  min- 
utes by  treating  fixed  cover-glass  preparations  with  a  concentrated  aqueous 
solution  of  methylene-blue,  after  which  they  are  washed  with  water,  dried 
between  filter-papers,  and  mounted  in  Canada  balsam. 

198.  The  e-  or  neutrophile  granules  which  are  found  normally  in 
the  polynuclear  leucocytes  of  man  (as  also  in  pus-cells),  in  some  of  the 
transitional  cells,  and  in  the  myelocytes,  are  stained  by  Ehrlich  as  follows  : 
5  vols.  of  a  saturated  aqueous  solution  of  acid  fuchsin  are  mixed  with  i  vol. 
of  a  concentrated  aqueous  solution  of  methylene-blue.      To  this  5  vols.  of 
water  are  added,  and  the  whole  allowed  to  stand  for  a  few  days,  after 
which  the  solution  is  filtered.     This  mixture  stains  in  five  minutes,  and 
the  specimen  is  then  washed  with  water,  etc.     The  neutrophile  granules 
are   colored  green,  the    eosinophile  granules   red  and    the   hemoglobin 
yellow. 

199.  Neutrophile  and  eosinophile  granules  may  also  be  stained  in 
Ehrlich' s  neutrophile  mixture  : 

Orange  G',  saturated  aqueous  solution,     .    .  130  to  135  c.c. 
Acid  fuchsin,    "  "  "  .    .    80  to  120 

Methyl-green,  "  "  "  .    .  125 

Distilled  water, 300 

Absolute  alcohol, 200 

Glycerin, 100 

Mix  the  above  quantifies  of  orange  G,  acid  fuchsin,  water,  and  alco- 
hol in  a  bottle  and  add  slowly,  while  shaking  the  bottle,  the  methyl -green 
and  finally  the  glycerin.  The  cover-glass  preparations  should  be  fixed  in 
the  ether  and  alcohol  solution  for  about  one  hour,  or  fixed  with  dry  heat 
at  a  temperature  of.uo°C.  for  from  fifteen  to  thirty  minutes.  Float 
the  preparation  on  a  small  quantity  of  the  stain  for'about  fifteen  minutes, 
wash  in  water,  dry  and  mount  in  balsam.  The  red  blood-cells  are  stained 
a  reddish -brown  color  (brick-color),  all  nuclei  a  light  blue-green,  the 
eosinophile  granules  a  fuchsin -red,  and  the  neutrophile  granules  a  violet- 
red.  Griibler,  of  Leipzig,  has  prepared  a  dry  powder,  known  as  the 
Ehrlich-Biondi-Heidenhain  three-color  mixture,  which  is  prepared  for 
use  by  making  a  0.4%  solution  in  distilled  water,  to  100  c.c.  of  which 
are  added  7  c.c.  of  a  0.5%  aqueous  solution  of  acid  fuchsin. 

200.  The  hemoglobin  shows  itself  in  the  form  of  crystals.      In  certain 
teleosts  the  crystals  are  formed  in  the  blood-corpuscles  around  the  nuclei 
and  often  within  a  short  time  after  death.      In  old  alcoholic  specimens,, 
hemoglobin  crystals  (blood  crystals)  are  found  in  the  vessels  and  were 
first  discovered  here  by  Reichert  in  the  blood  of  the  guinea-pig.     They 
have  been  found  in  large  quantities 'in  the  splenic  blood  of  a  sturgeon 
which  had  been  preserved  for  forty  years  in  alcohol.      The  hemoglobin 
crystals  belong   to  the  rhombic  series  of  crystallographic  classification. 
The  simplest  method  of  demonstrating  hemoglobin  crystals  is  probably 
the  following :  The  blood  is  first  defibrinated  by  whipping  or  agitating 
with  mercury,  after  which  process  sulphuric  ether  is  added,  drop  by  drop, 
until   the  mixture  has  been   made  laky ;    this  change  may  be  detected 


TECHNIC  (BLOOD    AND    BLOOD-FORMING    ORGANS).  2O/ 

macroscopically  by  the  sudden  change  from  an  opaque  to  a  dark,  trans- 
parent, cherry-red  color.  No  red  blood-cells  should  now  be  seen  under 
the  microscope.  The  preparation  is  placed  on  ice  for  from  twelve  to 
twenty-four  hours  after  which  a  drop  of  the  blood  is  placed  on  a  slide. 
In  half  an  hour  it  will  be  seen  that  the  margin  of  the  drop  has  begun  to 
dry.  A  cover-slip  is  now  applied  and,  after  a  few  minutes,  numerous 
crystals  are  seen  to  form  at  the  margin  of  the  drop,  a  process  which  may 
be  followed  under  the  microscope.  Large  hemoglobin  crystals  are  ob- 
tained by  Gscheidtlen  as  follows :  Defibrinated  blood  is  placed  in  a 
glass  tube,  which  is  then  hermetically  sealed.  The  blood  is  now  sub- 
jected .  to  a  temperature  of  about  40°  C.  for  two  or  three  days ;  if 
then  the  glass  be  broken  and  the  blood  poured  into  a  flat  dish,  large 
hemoglobin  crystals  are  immediately  formed. 

201.  Crystals  also  appear  if  a  drop  of  laky  blood  be  placed  in  a  thick 
solution  of  Canada  balsam  in  chloroform  and  covered  with  a  cover-slip. 

202.  Hemin  crystals    (Teichmann's 
crystals  ;    hemin  is  hematin-chlorid)  in 
the    shape    of  rhombic    plates   are    very 
easily  obtained  from  the  blood.      A  drop 

of  the  latter  is  placed  on  a  slide  and  care-       /- 
fully  mixed  with  a  small  drop  of  normal        .  .'  •- 
salt    solution.       This    is    then    carefully 
warmed  until   the  fluid    evaporates   and    .  N 

leaves    a    reddish  -  brown    residue,    after 

which  a  cover-glass  is  applied  and  glacial  V^\>    "• 

acetic  acid  added  until  the  space  between 
slide  and  cover-glass  is  filled.  The  prep- 
aration is  now  heated  until  the  acetic 
acid  boils.  As  soon  as  the  latter  evap- 
orates, Canada  balsam  may  be  brought 
under  the  cover-glass,  thus  producing  a  ; 

permanent  specimen.  When  fluids  or 
stains  suspected  of  containing  blood  are 
to  be  examined,  the  hemin  crystals  be- 
come of  the  utmost  importance,  as  their 

demonstration  is  then  a  positive  indication      Fig-  172.— Fibrin   from  laryngeal 
of  the  presence  of  blood.    Fluids  are  evap- 
orated and  treated  with  glacial  acetic  acid 

as  above  directed.  Suspected  blood  stains  on  cloth  are  treated  as  follows  : 
Small  pieces  are  cut  from  the  cloth  in  the  region  of  the  stain,  soaked  in 
normal  salt  solution,  and  the  resulting  fluid  treated  as  above.  If  the  stain 
is  on  wood  or  other  solid  object,  the  stain  is  scraped  off  and  dissolved  in 
normal  salt  and  then  tested  for  hemin  crystals.  Hemin  crystals  are  almost 
or  entirely  insoluble  in  water,  alcohol,  ether,  ammonia,  glacial  acetic 
acid,  dilute  sulphuric  acid,  and  nitric  acid.  They  are,  however,  soluble 
in  potassium  hydrate. 

203.  A  third  form  of  crystals  occasionally  found  in  the  blood  and 
frequently  in  the  corpora  lutea  and,  under  pathologic  conditions,  also  in 
apoplectic  areas,  are  the  hematoidin  crystals  first  discovered  by  Virchow. 
Masses  of  these  crystals  have  an  orange  color.      Microscopically,  they 
appear  as  red  rhombic  plates.     As  'they  are  soluble  in  neither  alcohol 
nor  chloroform,   they  are  easily    preserved    in  Canada  balsam.      Their 


2O8  THE    CIRCULATORY    SYSTEM. 

artificial  production  has  as  yet  never  been  accomplished.      Hematoidin 
contains  no  iron. 

204.  The   fibrin   thrown  down  when  the  blood   coagulates  may  be 
demonstrated  upon  the  slide  in  the  form  of  very  fine  particles  and  fila- 
ments.    A  drop  of  blood  is  brought  upon  the  slide  and  kept  for  a  time  in 
a  moist  chamber  or  on  the  table  until  it  begins  to  clot ;    after  which  a 
cover-slip  is  applied  and  the  preparation  washed  with  water  by  continued 
irrigation.      In  this  manner  most  of  the  red  blood-corpuscles  are  removed. 
Lugol  solution  may  now  be  added,  which  stains  brown  the  filaments  of 
the  fibrin  network  adherent  to  the  slide.      In  order  to  see  the  fibrin  net- 
work in  sections,  it  is  better  to  use  specimens  previously  fixed  in  alcohol ; 
the  sections  are  stained  for  ten  minutes  in  a  concentrated  solution  of  gen- 
tian-violet in  anilin  water  (Weigert),   rinsed  in  normal    salt    solution, 
treated  for  about  ten  minutes  with  iodo-iodid  of  potassium  solution,  and 
then  spread  upon  a  slide  and  dried  with  filter-paper.     They  are  now 
placed  in  a  solution  consisting  of  2  parts  of  anilin  oil  and  i  part  of  xylol 
until  they  become  perfectly  transparent.     This  solution  is  then  replaced 
by  pure  xylol  and   finally  by  Canada   balsam.     The   fibrin  network  is 
stained  a  deep  violet. 

205.  There  are  different  methods  and  a  variety  of  material  at  our  dis- 
posal for  the  demonstration  of  the  blood  current  through  the  vessels.     The 
best  object  for  this  purpose  is  probably  the  frog.     The  procedure  is  as 
follows  :    The  animal  is  immobilized  by  poisoning  with  curare.      ^  gm. 
of  a  i  °lo  aqueous  solution  injected  into  the  dorsal  lymph -sac  will  immobilize 
the  frog  in  a  short  time.     The  exact  dose  can  not,  however,  be  given,  as 
the  commercial  curare  is  not  a  uniform  chemical  compound ;    the  dose 
must  therefore  be  ascertained  by  experiment.     As  is  well  known,  curare 
affects  exclusively  the  nerve  end -organs  of  striated  voluntary  muscle,  but 
does  not  affect  either  the  heart  muscle  or  unstriated  muscular  tissue  ;  hence 
the  utility  of  curare  for  this  purpose.     In  order  to  see  the  blood  current, 
it  is  only  necessary  to  stretch  the  transparent  web  between  the  frog's  toes 
and  fasten  it  with  insect  needles  to  a  cork  plate  having  a  suitable  open- 
ing.    If  the  cork  plate  be  large  enough  to  accommodate  the  whole  frog, 
it  may  be  placed  in  such  a  position  that  its  opening  lies  over  that  in  the 
stage  of  the  microscope.     The  web  thus  spread  out  may  be  examined 
with  a  medium  magnification.     The  tongue  of  the  frog  is  also  used  for  the 
same  purpose.     As  the  latter  is  attached  to  the  anterior  angle  of  the  lower 
jaw,   it  may  be  conveniently  drawn  out,   suitably  stretched,  and  then 
placed  over  the  hole  in  the  cork  plate.     A  very  good  view  of  the  circula- 
tion may  be  obtained  by  examining  the  mesentery  of  a  frog.     The  migra- 
tion of  the  leucocytes  through  the  vessel -walls  can  also  be  studied  in  such 
preparations.     An  incision  0.5  cm.  in  length  is  made  in  the  right  axillary 
line  through  the  skin  of  a  frog  (best  in  the  male),  care  being  taken  not  to 
injure  any  vessels  (which  can  be  seen  through  the  skin  in  frogs  possessing 
little  pigment).     The  abdominal  muscles  are  then  incised  and  a  pair  of 
forceps  introduced  to  grasp  one  of  the  presenting  intestinal  loops.     The 
latter  is  then  attached  to  the  cork  plate  with  needles,  and  the  mesentery 
carefully  stretched  over  the  opening.      On  examining  the  specimen  it  is 
best  to  moisten  it  with  normal  salt  solution  and  to  cover  the  area  to  be 
examined  with  a  fragment  of  a  cover-glass.     The  lung  may  also  be  exam- 
ined, but  here  the  incision  must  be  farther  forward. 

206.  To  obtain  a  general  idea  of  the  structure  r    lymphatic  glands,. 


TECHNIC  (BLOOD  AND  BLOOD-FORMING  ORGANS).  209 

sections  are  made  of  small  glands  fixed  in  alcohol  or  corrosive  sublimate. 
They  are  then  stained  with  hematoxylin  and  eosin.  In  such  preparations 
the  cortical  and  medullary  substances  can  be  studied  ;  the  trabeculae  and 
blood  take  the  eosin  stain. 

207.  The  flattened  endothelial  cells  covering  the  trabeculse  are  brought 
to  view  by  injecting  a  o.  i  %  solution  of  silver  nitrate  into  a  fresh  lymph- 
atic gland.     After  half  an  hour  the  gland  is  fixed  with  alcohol  and  car- 
ried through  in  the  regular  way  ;    the  sections  should  be  quite  thick  (not 
under  20  /^).     After  the  sections  have  been  mounted  in  Canada  balsam 
and  exposed  to  light  for  a  short  time,  the  endothelial  mosaic  will  be  seen 
wherever  the  silver  nitrate  has  penetrated. 

208.  Fixing  with  Flamming' s  solution  and  staining  with  safranin  is 
the  best  method  for  studying  the  germ  centers  of  the  lymph-follicles. 
Other  fluids  which  bring  out  the  mitoses  may  also  be  employed. 

209.  Reticular  tissue  is  best  demonstrated  by  sectioning  a  fresh  gland 
with  a  freezing  microtome,  removing  a  section  to  a  test-tube  one-quarter 
filled  with  water,  and  agitating  it.     The  lymphocytes  are  thus  shaken  out 
of  the  meshes  of  the  reticulum,  leaving  the  latter  free  for  examination. 

210.  The  same  results  can  be  obtained  by  placing  a  section  prepared 
in  the  above-named  manner  upon  a  slide,  wetting  it  with  water,  and 
carefully  going  over  it  with  a  camel' s-hair  brush.     The  lymphocytes  ad- 
here to  the  brush.      Both  methods  (His,  61)  may  be  applied  to  hardened 
sections  which  have  lain  in  water  for  a  day  or  so.      In  this  case,  how- 
ever, the  removal  of  the  lymphocytes  is  not  so  easy  as  in  fresh  sections. 

211.  In  thick  sections  the  reticulum  is  hidden  by  the  lymphocytes. 
If,  on  the  other  hand,  very  thin  sections  (not  over  3  /*)  be  made,  especially 
of  objects  fixed  in  Flemming's  solution,  the  adenoid  reticulum  stands  out 
clearly  without  any  further  manipulation. 

212.  The  reticular  structure  may  also  be  demonstrated  by  an  artificial 
digestion  of  the  sections  with  trypsin.     The  sections  are  then  agitated  in 
water,  spread  on  a  slide,  dried,  then  moistened  with  a  picric  acid  solu- 
tion (i  gm.  in  15  c.c.  of  alcohol  and  30  c.c.  of  water),  again  dried,  cov- 
ered with  a  few  drops  of  fuchsin  S  solution  (fuchsin  S  i  gm.,  alcohol 
33  c.c.,  water  66  c.c.),  and  left  to  stand  for  half  an  hour.     The  fuchsin 
solution  is  then  carefully  removed,  the  section  washed  again  for  a  short 
time  in  the  same  picric  acid  solution,  then  treated  with  absolute  alcohol, 
xylol,  and  finally  mounted  in  Canada  balsam.     The  reticular  tissue  of 
both  lymphatic  glands  and  spleen  are  stained  a  beautiful  red   (F.    P. 
Mall). 

213.  The  treatment  of  splenic  tissue  is  practically  the  same  as  that  of 
the  lymphatic  glands. 

214.  In  all  these  organs  (lymph- glands,  spleen,  and  bone-marrow)  a 
certain  amount  of  fluid  may  be  obtained  by  scraping  the  surface  of  the 
fresh  tissue.     This  may  then  be  examined  in  the  same  manner  as  blood 
and  lymph  (see  Technic  of  same).      Sections  of  lymph -glands  and  spleen 
previously   fixed  in  alcohol,  mercuric  chlorid,  or  even  in    Flemming's 
solution  may  be  examined  by  the  granula  methods  of  Ehrlich. 

215.  By  using  the  chrome-silver  method  a  peculiar  network  of  retic- 
ular fibers  may  be  seen  in  the  spleen.      (Gitterfasern  ;   Oppel,  91.) 

216.  The  examination  of  the  bone-marrow  belongs  also  to  this  chap- 
ter.    The  marrow  of  the  diaphysis  is  taken  out  by  splitting  the  bone 

14 


2IO  THE    DIGESTIVE    ORGANS. 

longitudinally  with  a  chisel.  With  a  little  practice,  it  is  easy  to  obtain 
small  pieces  of  the  marrow,  which  are  then  fixed  by  the  customary 
methods  and  cut  into  sections.  In  the  epiphysis  the  examination  is 
confined  either  to  the  pressing  out  of  a  small  quantity  of  fluid  with  a  vice, 
or  to  the  decalcification  of  small  masses  of  spongy  bone,  containing  red 
bone-marrow.  In  the  first  case,  methods  applicable  to  blood  examina- 
tion are  employed  ;  in  the  second,  section  methods  (see  also  the  petrifi- 
cation  method,  T.  158)  are  used.  The  methods  given  for  the  prepara- 
tion of  lymph-glands  and  spleen  are  also  applicable  in  many  cases. 

217.  Enderlen  has  demonstrated  reticular  fibers  (Gitterfasern)  in  the 
bone-marrow  by  means  of  the  chrome-silver  method. 

TECHNIC  (CIRCULATORY  SYSTEM). 

218.  To  obtain  a  topographical  view  of  the  layers  composing  the 
heart  and  vessels,  sections  are  made  of  tissues  that  have  been  fixed  in 
Miiller's  fluid,  chromic  acid,  etc.      If  the  specimens  are  to  be  studied  in 
detail,  small  pieces  must  be  used,  and  are  best  fixed  in  chromic-osmic 
mixtures  or  corrosive  sublimate.      Celloidin  imbedding  is  recommended 
for  general  topographic  work.     The  further  treatment  is  elective. 

219.  The  endothelium  of  the  intima  may  be  brought  to  view  by  silver 
nitrate  impregnation  methods,  by  injecting  silver  solutions  into  the  vascu- 
lar system,  etc.  (vid.  T.  109).     The  endothelial  elements  of  the  smallest 
vessels  and  capillaries  are  then  clearly  defined  by  lines  of  silver.      Larger 
vessels  must  be  cut  open,  the  intima  separated,  and  pieces  of  its  lamellae 
examined. 

220.  With  regard  to  the  isolation  of  the  muscle-cells  of  the  myocar- 
dium and  of  the  walls  of  the  vessels,  see  T.  170  to  172. 

221.  Elastic  elements,  plates  and  networks  are  best  observed  in  the 
tunica  media  of  the  vessels,  very  small  pieces  of  which  are  treated  for 
some  hours  with  33%  potassium  hydrate. 

222.  The  appropriate  stains  for  section  work  are  those  which  bring 
out  the  elastic  elements  and  the  smooth  muscle-cells.      For  the  former, 
orcein  is  used  (vid.  T.  138). 

223.  For  demonstrating  the  distribution  of  the  capillaries,  the  reader 
is  referred  to  the  injection  methods  (vid.  T.  100  et  seq. )     The  lymph- 
capillaries  are  injected  by  puncture  (T.  in)  ;  compare  also  the  methods 
of  Altmann  (T.  112). 


III.    THE  DIGESTIVE  ORGANS. 

THE  intestinal  canal  with  the  glands  derived  therefrom  originates 
from  the  inner  layer  of  the  blastoderm,  the  entoderm.  The  latter, 
however,  does  not  extend  to  the  external  openings  of  the  body,  as 
the  ectoderm  forms  depressions  at  these  points  which  grow  inward 
toward  the  still  imperforate  fore  and  hind  gut  to  communicate 
finally  with  its  lumen.  This  applies  as  well  to  the  formation  of 
the  primitive  oral  cavity,  which  is  separated  only  secondarily  into 
oral  and  nasal  cavities,  as  to  the  anus.  The  anterior  boundary 


THE   ORAL   CAVITY.  211 

between  the  ectodermal  and  entodermal  portions  of  the  digestive 
tube  consists  of  a  plane  passing  through  the  opening  of  the  pos- 
terior nares  and  continued  downward  along  the  palatopharyngeal 
arch.  Everything  lying  anterior  to  this  is  of  ectodermal  origin, 
therefore  the  entire  oral  and  nasal  cavities  with  their  derivatives. 
The  lining  of  these  cavities  consists,  however,  of  a  true  mucous 
membrane,  closely  resembling  in  its  structure  that  of  the  intestinal 
tract. 

A.  THE  ORAL  CAVITY. 

The  epithelium  of  the  oral  mucous  membrane  is  of  the  stratified 
squamous  type,  differing  from  the  epithelium  of  the  epidermis 
in  that  the  stratum  granulosum  does  not  appear  here  as  an  inde- 
pendent layer.  The  stratum  lucidum  is  also  wanting,  and  the 
cornification  of  the  layer  analogous  to  the  stratum  corneum  of  the 
skin  is  not  complete  (compare  Skin).  In  the  mucous  membrane 
the  cells  of  even  the  most  superficial  layers  contain  nuclei,  which, 
although  partly  atrophied,  still  show  chromatin,  and  as  a  conse- 
quence are  easily  demonstrated. 

Beneath  the  epithelium  lies  a  tissue  of  mesodermic  origin,  also 
belonging  to  the  mucous  membrane  and  known  as  the  mucosa  or 
stratum  proprinm  (lamina  propria,  tunica  propria),  in  which  nu- 
merous glands  are  situated.  The  mucosa  consists  of  a  fibrillar 
connective  tissue  with  few  elastic  fibers,  and  of  adenoid  tissue 
containing  numerous  lymphoid  cells ;  essentially,  therefore,  a 
diffusely  distributed  adenoid  tissue  with  occasional  lymph-follicles 
imbedded  in  its  substance.  The  mucosa  presents  numerous 
papillae,  which  are  either  simple  or  compound  (branched)  eleva- 
tions of  the  mucosa,  varying  in  length  and  density,  according  to 
their  location  and  extending  for  variable  distances  into  the  over- 
lying epithelium.  As  in  the  papillary  layer  of  the  corium  (see 
Skin),  so  also  here  the  superficial  layer  of  the  stratum  proprium 
contains  very  fine  elastic  and  connective-tissue  elements  which  con- 
tribute to  the  structure  of  the  papillae.  All  these  papillae  contain 
capillaries  and  arterioles  which  are  derived  from  an  arterial  network 
in  the  mucosa.  The  lymphatics  are  similarly  arranged. 

At  the  red  margin  of  the  lips  the  papillae  are  unusually  high 
and  are  covered  at  their  summits  by  a  veiy  thin  epithelial  layer 
(Fig.  173).  Besides  the  sebaceous  glands  which  lie  at  the  angles 
of  the  mouth,  and  whose  ducts  open  at  the  surface,  there  are  here 
no  other  glandular  structures.  In  the  mucosa  of  the  mucous 
membrane  of  the  lips  and  cheeks  the  papillae  are  low  and  broad  ; 
here  also  open  the  ducts  of  compound  lobular,  alveolar  glands,  the 
gtanduld  labiates  and  buccales  whose  structure  is  similar  to  that  of 
the  large  salivary  glands  (see  these).  The  gums  possess  very  long 
and  attenuated  papillae,  covered  by  a  very  thin  layer  of  epithelium, 
therefore  bleeding  at  the  slightest  injury.  That  part  of  the  gum 


212 


THE    DIGESTIVE    ORGANS. 


covering  the  tooth  has  no  papillae.  The  gums  contain  no  glands. 
The  papillae  of  the  hard  palate  are  arranged  obliquely,  with  their 
points  directed  toward  the  opening  of  the  mouth.  The  papillae  of 
the  soft  palate  are  very  low  and  may  even  be  absent.  They  are 
somewhat  higher  on  the  anterior  surface  of  the  uvula.  (On  the 
posterior  surface  of  the  latter  occur  ciliated  epithelia  distributed  in 
islands  between  the  areas  of  stratified  squamous  epitheliumT)  In 
the  soft  palate  and  uvula  are  found  small  mucous  glands. 

Under  the  mucous  membrane  there  is  a  layer  consisting  princi- 


Transitipnal  zone  with 
irregular  papillae. 


Mucous  : — 
mem  -  ^ 
brane  \ 
w  ith  \ 
high  i 
papil-  I 


vf 


Duct  of 

gland. 

Epithe- 

Hum 
of  mu- 
cous 
mem- 
brane. 

Gland. 


i    fied  ep- 
/    iderm- 


.'-  Striated 
muscle. 


Hairfol- 
licles. 

Epider  - 
mis. 


Fig.  173. — Section  through  the  lower  lip  of  man  ;  X  J8. 

pally  of  connective  tissue  and  elastic  fibers,  the  submucosa  (stratum 
submucosum,  tela  submucosa).  In  the  mucous  membrane  of  the 
mouth  the  transition  of  the  tissue  of  the  mucosa  into  that  of  the 
submucosa  is  very  gradual.  The  submucosa  of  the  hard  palate  is 
closely  connected  with  the  periosteum  and  contains,  especially  at 
its  posterior  portion,  numerous  glands.  In  other  regions  of  the 
mouth  (lip)  the  glands  extend  also  into  the  submucosa.  The 
mucosa  and  epithelium  lining  the  mouth  cavity  are  richly 
supplied  with  nerves  which  terminate  either  in  special  sensory 


THE   ORAL   CAVITY.  213 

nerve-endings  or  in  free  sensory  nerve-endings,  or  on  the  blood- 
vessels. In  the  papillae  of  the  mucosa  are  found  corpuscles  of 
Krause.  (See  p.  154.)  The  nerves  terminating  in  free  sensory 
endings  are  the  dendrites  of  sensory  neurones  (medullated  sensory 
nerves),  which,  while  yet  medullated,  branch  and  form  plexuses 
with  large  meshes,  situated  in  the  submucosa  and  deeper  portion  of 
the  mucosa.  The  medullated  branches  of  the  nerve-fibers  constitut- 
ing these  plexuses  proceed  toward  the  epithelium,  dividing  further 
in  their  course.  Immediately  under  the  epithelium  the  medullated 
branches  lose  their  medullary  sheaths,  divide  further,  and  form  the 
subepithelial  plexuses.  The  nonmedullated  branches  enter  the 
epithelium,  where  they  form  telodendria  (end-brushes),  the  terminal 
branches  of  which  surround  the  epithelial  cells,  between  which 
they  end  either  in  very  fine  granules  or  in  small  groups  of  such,  or, 
again,  in  variously  shaped  end-discs.  (See  Fig.  130.)  The  blood- 
vessels are  richly  supplied  with  vasomotor  nerves,  the  neuraxes 
of  sympathetic  neurones,  which  terminate  on  the  muscle-cells  of 
the  vessels.  In  the  adventitia  are  also  found  free  sensory  nerve- 
endings.  (See  Fig.  170.) 

J.  THE  TEETH. 

Structure  of  the  Adult  Tooth. — The  adult  tooth  is  made  up 
of  three  substances — the  enamel,  the  dentin,  and  the  cementum.  The 
latter  covers  that  part  of  the  tooth  within  the  alveolar  process  of 
the  jaw  and  also  the  root  of  the  tooth.  The  enamel  caps  that  part 
of  the  tooth  projecting  into  the  oral  cavity,  the  crown  of  the  tooth. 
The  neck  of  the  tooth  is  the  region  where  the  cementum  and 
enamel  eome  in  contact.  The  greater  part  of  the  tooth  consists  of 
dentin,  which  is  present  in  the  crown  as  well  as  in  the  root.  All 
the  substances  of  the  tooth  just  mentioned  become  very  hard  from 
the  deposition  of  lime -salts.  Every  tooth  contains  a  cavity  sur- 
rounded by  dentin,  the  pulp  cavity,  or  dental  cavity.  This  is  filled 
with  a  soft  tissue,  the  pulp,  consisting  of  while  fibrous  tissue,  ves- 
sels, and  nerves.  That  part  of  the  pulp  cavity  lying  in  the  axis  of 
the  fang  is  called  the  root-canal ;  by  an  opening  in  the  latter  (fora- 
men apicis  dentis)  the  pulp  is  connected  with  the  periosteal  con- 
nective tissue  of  the  dental  alveolus. 

The  enamel  is  a  very  hard  substance,  the  hardest  in  the  body, 
and  may  be  compared  to  quartz.  In  uninjured  teeth  the  enamel  is 
covered  by  an  exceedingly  thin,  structureless  enamel  membrane 
(cuticula  dentis).  The  enamel  contains  very  little  organic  substance 
(from  3  <f0  to  5  yc),  in  consequence  of  which  it  is  soluble  in  acids  with 
scarcely  any  residue.  The  elements  composing  it  are  prismatic 
columns,  the  enamel  prisms,  which  occupy  the  whole  thickness  of 
the  enamel  from  the  superficial  membrane  to  the  dentin.  .  These  are 
not  thicker  at  the  surface  of  the  tooth  than  at  the  dentin,  and  in 
transverse  section  show  a  hexagonal  or  polygonal  shape.  They  are 


214 


THE    DIGESTIVE    ORGANS. 


Enamel. 


j»; Pulp  cavity. 


joined  to  each  other  by  a  cement-substance  which  is  somewhat 
more  resistant  than  the  substance  of  the  prisms  themselves.  In  the 
adult  they  are  entirely  homogeneous,  but  in  embryos  and  even  in 
the  new-born  they  show  a  (fibrillar)  longitudinal  striation.  In  their 
course  through  the  thickness  of  the  enamel  they  change  their 

direction  by  a  series  of 
symmetrical  curves,  and 
cross  each  other  in  groups 
in  a  typical  manner.  There 
are  also  seen  in  the  enamel 
the  parallel  lines  known  as 
the  lines  of  Retzius  (see 
Fig.  174),  which  are  to  be 
regarded  as  traces  of  the 
strata  caused  by  the  peri- 
odic deposition  of  lime- 
salts  ;  they  are  very  vari- 
able, as  their  structure 
depends  on  the  nutritive 
condition  during  the  depo- 
sition of  the  lime  -  salts 
(Berten). 

The  dentin  is,  next  to 
the  enamel,  the  hardest 
tissue  of  the  tooth.  After 
its  decalcification  a  sub- 
stance is  left  which  yields 
gelatin.  The  dentin  is 
permeated  by  a  system 
of  canals  having  usually 
a  transverse  direction,  the 
so-called  dentinal  tubules, 
which  are  from  1.3  //  to 
4.5  fj.  in  diameter.  These 
originate  in  the  pulp  cav- 
ity, and  during  their  course 
become  slightly  curved, 
like  the  letter  S-  At  their 
outer  third  they  branch 
and  become  constantly 
smaller.  As  a  rule,  they 
extend  as  far  as  the  en- 
amel, although  a  few  now  and  then  even  cross  the  boundary  of  the 
enamel.  (They  never  reach  the  cement,  but  leave  here  a  free  zone 
in  which  trie  ground-substance  of  the  dentin  alone  is  present.  The 
dentinal  tubules  possess  sheaths,  the  sheaths  of  Neumann,  which 
may  be  isolated,  analogous  to  the  sheaths  of  the  canaliculi  of  bone, 
and  which  contain  throughout  their  entire  length  filiform  prolonga- 


-  Dentin. 


Cementum. 


Fig.  174. — Scheme  of  a  longitudinal  section 
through  a  human  tooth.  In  the  enamel  are  seen 
the  "lines  of  Retzius." 


THE    TEETH. 


215 


tions  of  certain  pulp-cells  (odontoblasts),  the  dcntinal  fibers.  Ac- 
cording to  v.  Ebner,  the  ground-substance  of  the  dentin  consists  of 
bundles  of  connective-tissue  fibrils,  which  in  the  root  run  parallel  to 
the  long  axis  of  the  tooth,  and  in  the  crown  have  a  direction  at  right 
angles  to  that  of  the  dentinal  tubules.  The  S-shaped  curves  of  the 
latter  give  rise  to  the  lines  of  Schrager  in  the  dentin,  which  are 
visible  with  an  ordinary  magnifying  glass.  Peculiar,  irregularly 
branched  spaces  are  often  seen  in  the  dentin.  These  are  the  inter- 
globular  spaces,  and  represent  areas  in  which  calcification  has  not 
taken  place. 

The  cementum  is  closely  adherent  to  the  dentin,  and  consists  of 


Interglobular 
space. 


—    Enamel. 


._    Branching  of  the 
dentinal  tubules. 


—    Dentinal  tubules. 


Fig.  175. — A  portion  of  a  ground  tooth  from  man,  showing  enamel  and  dentin  ;  X  I7°- 

Technic  No.  225. 


bone  tissue,  the  parallel  lamellae  of  which  contain,  as  a  rule,  no 
Haversian  canals.  There  occur,  however,  cement  lamellae,  which 
in  places  lose  their  bone-cells.  A  peculiarity  of  the  cementum  is 
the  presence  of  a  large  number  of  Sharpey's  fibers,  which  are 
especially  abundant  in  those  areas  containing  no  bone-corpuscles. 
These  fibers  are  usually  found  in  an  uncalcified  condition. 

The  tooth-pulp  is  a  tissue  resembling  (embryonic  connective  tis- 
sue,} consisting  of  connective -tissue  fibrils,  branched  connective- 
tissue  cells,  and  a  semifluid,  interfibrillar  ground-substance.  It  is 
characteristic  of  this  tissue  that  the  fibrils  never  join  to  form  con- 
nective-tissue fibers.  At  the  surface  of  the  pulp  is  a  continuous 


2l6 


THE    DIGESTIVE    ORGANS. 


layer  of  cells,  the  odontoblasts.  These  are  columnar  cells  with 
basal  nuclei  and  two  or  three  processes  extending  into  the  can- 
aliculi  of  the  dentin,  forming  here  the  dentinal  fibers  already  de- 
scribed. As  a  rule,  the  odontoblasts  also  send  a  single  fiber  into 
the  pulp.  These  may  intertwine  and  give  rise  to  a  network  within 
its  substance. 

The  tooth  is  joined  to  the  periosteum  of  the  alveolus  by  a  re- 
duplication of  the  latter  over  its  root,  the  dental  periosteum  or 
peridental  membrane.  This  consists  of  bundles  of  connective 
tissue  (elastic  fibers  are  here  absent)  directly  continuous  with 
Sharpey's  fibers  in  the  cementum.  At  the  neck  of  the  tooth  the 
peridental  membrane  disappears  in  the  submucosa  of  the  gum  ;  in 


'«v~  -  b 


Fig.  176. — A,  Longitudinal  section  through  a  human  molar  from  the  center  of  the 
enamel  layer,  decalcified  with  dilute  hydrochloric  acid  ;  B,  tangential,  C,  radiate,  and 
D,  transverse  section  through  the  dentin  of  a  human  tooth,  showing  the  fibrillar  struc- 
ture of  the  ground-substance  (taken  from  v.  Ebner,  91)  :  <?  and  b,  Two  layers  in  which 
the  direction  of  the  enamel  prisms  changes ;  in  c  is  seen  a  dentinal  fiber  with  its  sheath  ; 
e,  groups  of  fibrils  ;  d,  dentinal  tubules. 

the  former  are  found  here  and  there  peculiar  masses  of  epithelial 
cells  representing  the  remains  of  the  enamel  organs. 

The  tooth-pulp  has  a  rich  blood  supply.  A  small  artery  enters 
the  pulp  cavity  through  the  apical  foramen,  which,  as  it  passes  up 
through  the  pulp,  gives  off  numerous  smaller  branches  which  end 
in  a  capillary  network  situated  under  the  layer  of  odontoblasts. 
Numerous  medullated  nerve -fibers  (dendrites  of  sensory  neurones) 
enter  the  pulp  cavity  through  the  apical  foramen.  Some  of  these 
lose  their  medullary  sheaths  soon  after  entering,  or  just  before 
entering,  the  pulp,  and  divide  into  long,  fine,  varicose  fibers  which 
interlace  to  form  a  loose  plexus  under  the  odontoblasts.  Other 


THE    TEETH. 


217 


Cementum. 


medullated  fibers,  grouped  into  small  bundles,  ascend  in  the  pulp 
for  variable  distances  ;  the  nerve-fibers  of  the  bundles  then  sepa- 
rate and  as  single  fibers  approach  the  superficial  portion  of  the 
pulp,  and,  after  losing  their  medullary  sheaths,  divide  into  fine 
varicose  fibers  forming  under  the  odontoblasts  a  plexus  continuous 
with  the  plexus  above  mentioned.  From  the  varicose  nerve-fibers 
of  this  plexus  small  terminal  branches  are  given  off  which  termi- 
nate between  the  odontoblasts,  or  pass  through  the  layer  of 
odontoblasts,  to  end  between  these  and  the  dentin  (Retzius,  94 ; 
Huber,  98).  Medullated  nerve-fibers  also  terminate  in  free  end- 
ings in  the  peridental  membrane. 

Development  of  the  Teeth. — In  the  second  month  of  fetal 
life  the  first  traces  of  the  teeth  are  seen  in  the  development  of  a 
groove  along  the  inner  edge  of  the  fetal  jaw,  the  dentinal  or  en- 
amel groove.  From  the  floor  of  the  latter  an  epithelial  ridge 
is  formed  constituting  the  anlage  of  the  enamel  organs  and 
known  as  the  dentinal  ridge,  or  enamel  ledge.  At  those  points 
at  which  the  fiAk -teeth  later  appear,  the  enamel  ledge  develops 
solid  protuberances  corre- 
sponding in  number  to  the 
temporary  teeth.  These  are 
known  as  the  dentinal  bulbs 
or  enamel  gentis.  In  their 
first  stage  of  development 
the  enamel  germs  are  knob- 
like,  but  later  their  bases 
spread,  and  they  become 
flattened  and  finally  cup- 
shaped  by  the  pushing  up 
into  them  of  connective  - 
tissue  projections,  the  den- 
tinal papilla.  At  the  same 
time  they  gradually  sink 
deeper  into  the  underlying 
tissue,  but  still  remain  con- 
nected, by  means  of  a  thin 
cord,  with  the  epithelium  of 
the  enamel  ledge,  which  now  lies  on  the  inner  side  of  the  enamel 
germs.  The  enamel  germs  now  differentiate  into  enamel  organs. 
In  this  stage  they  consist  of  an  outer  layer  of  columnar  epithelial 
cells,  which  are  to  be  regarded  as  a  direct  continuation  of  the  basal 
cells  from  the  epithelium  of  the  oral  mucous  membrane,  or  still 
better,  of  the  enamel  ledge  ;  the  epithelium  in  the  interior  of  the 
organ  is  derived  from  the  stratum  Malpighii  of  the  oral  epithe- 
lium. The  cells  of  this  layer,  however,  undergo  a  change  in 
shape  and  structure,  in  that  an  increased  quantity  of  lymph-plasma 
or  intercellular  substance  collects  in  the  interspinous  spaces  between 
the  cells,  pushing  the  cells  apart,  and  allowing  their  processes  to 


Dentin. 


Fig.  177. — Cross-section  of  human  tooth, 
showing  cement  and  dentin;  X212-  Technic 
No.  225  (vid.  also  Technic  152).  At  a  are  seen 
small  interglobular  spaces  (Tomes'  granular  layer). 


2l8  THE    DIGESTIVE    ORGANS. 

develop  until  the  cells  finally  assume  a  stellate  shape.  In  this  way 
the  enamel  pulp  is  gradually  formed.  The  next  stage  is  character- 
ized by  a  vertical  growth  of  the  dentinal  papillae,  which  soon  be- 
come surrounded  on  all  sides  by  the  cap-like  enamel  organs.  -  The 
cylindric  cells  (enamel  cells)  of  the  enamel  organs  lying  next  to 
the  papillae  become  lengthened,  and  after  passing  through  further 
changes,  finally  develop  into  the  enamel  prisms  of  the  teeth.  At 
the  periphery  of  the  dentinal  papillae,  there  is  differentiated  a  layer 
of  columnar  cells,  the  odontoblasts,  which  have  a  connective -tissue 
origin,  and  later  form  the  dentin.  During  these  processes  a 
connective -tissue  mantle,  the  dental  sac,  rich  in  cellular  and  fibrous 
elements,  is  formed  around  each  tooth  anlage. 

The  earliest  appearance  of  the  enamel  is  in  the  form  of  a  cuticu- 
lar  membrane,  developed  from  the  ends  of  the  enamel  cells  resting 
on  the  dentinal  papilla,  this  cuticular  membrane  appearing  in  the  form 
of  a  thin  layer  covering  the  top  of  the  dentinal  papilla.  Sometime 
later,  short  striated  processes — 7 ernes'  processes — appear  on  the 


,    .„. .,-,, ,,,.,.-».«,™..,x  ,-  ,,^,,.,,,  '"      Odontoblasts. 

odontoblasts'  ""'iwii^       ii 

Terminal  nerve- 
Terminal  nerve- 
fiber. 


Fig.  178. — Nerve  termination  in  the  pulp  of  a  rabbit's  molar,  stained  in  methylene- 
blue  (intra  vitavi]  :  a,  Odontoblasts  seen  in  side  view  ;  b,  a  number  of  odontoblasts  seen 
in  end  view,  showing  a  terminal  branch  of  a  nerve-fiber  situated  between  the  odonto- 
blasts and  the  dentin  (Huber,  "Dental  Cosmos,"  October,  1898). 

lower  end  of  each  of  the  enamel  cells  (the  end  toward  the  dentinal 
papilla).  These  are  imbedded  in  a  cement-substance,  forming  a 
continuous  layer.  The  Tomes'  processes  are  regarded  as  the  be- 
ginnings of  the  enamel  prisms.  Calcification  begins  in  the  middle 
of  these  processes  ;  they  thicken  at  the  expense  of  the  cement- 
substance  surrounding  them,  which  later  also  calcifies.  The  enamel 
as  a  whole  thickens  by  the  elongation  of  the  Tomes'  processes  of 
the  enamel  cells  and  by  their  subsequent  calcification.  The  process 
ends  finally  in  the  death  and  partial  absorption  of  the  enamel  cells 
and  the  remaining  elements  of  the  enamel  organs  ;  these  structures 
persist  for  a  short  time  after  the  eruption  of  the  tooth  as  a  cuticular 
sheath. 

The  dentin  is  developed  by  the  odontoblasts  by  a  process 
analogous  to  that  observed  in  the  formation  of  bone  by  the  osteo- 
blasts.  These  epithelioid  cells  secrete  at  their  outer  surfaces  a 


Fig.  181. 


Fig.  182. 


Figs.  179-182. — Four  stages  in  the  development  of  a  tooth  in  a  sheep  embryo  (from 
the  lower  jaw)  :  Fig.  179,  Anlage  of  the  enamel  germ  connected  with  the  oral  epithelium 
by  the  enamel  ledge;  Fig.  180,  first  trace  of  the  dentinal  papilla;  Fig.  181,  advanced 
stage  with  larger  papilla  and  differentiating  enamel  pulp  ;  Fig.  182,  budding  from  the 
enamel  ledge  of  the  anlage  of  the  enamel  germ,  which  later  goes  to  form  the  enamel  of 
a  permanent  tooth  ;  at  the  periphery  of  the  papilla  the  pdontoblasts  are  beginning  to 
differentiate.  Figs.  179,  180,  and  181,  X  IIO5  Fig.  182,  X  4°-  a,  a,  a,  a,  Epithelium 
of  the  oral  cavity  ;  b,  b,  b,  &,  its  basal  layer ;  c,  <:,  c,  the  superficial  cells  of  the  enamel 
organ;  d,d,d,d,  enamel  pulp;  /,/,/,  dentinal  papilla;  s,  s,  enamel-forming  elements 
(enamel  cells)  ;  o,  odontoblasts  ;  S,  enamel  germ  of  the  permanent  tooth  ;  vy  part  of  the 
enamel  ledge  of  a  temporary  tooth  ;  u,  surrounding  connective  tissue. 

219 


220 


THE    DIGESTIVE    ORGANS. 


,« 


Enamel  pulp. 


Enamel  cells. 


homogeneous  substance  which  fuses  to  form  a  continuous  layer, 
the  membrana  prceformativa.  The  further  development  of  the  dentin 
is  as  follows  :  Its  ground-substance  is  deposited  at  the  cost  of  the 
lateral  portions  of  the  odontoblasts  (under  the  membrana  praeforma- 
tiva),  the  axial  portion  of  the  cells  remaining  intact  as  the  dentinal 
fibers  ;  the  basal  portions  of  the  cells  containing  the  nuclei  persist, 
later  constituting  the  odontoblasts  of  the  adult  pulp.  By  the  fusion 
of  the  segments  of  the  ground-substance  formed  by  each  cell,  it 
becomes  a  -homogeneous  mass,  but  soon  displays  connective-tissue 
fibrils  which  gradually  undergo  a  process  of  calcification.  The  mem- 
...  bran  a  praeformativa  has 

^  no    fibers    and    calcifies 

much  later.  It  lies  im- 
mediately beneath  the 
enamel  or  the  cementum, 
and  in  the  normal  tooth 
always  contains  small  in- 
terglobular  spaces.  In 
the  adult  tooth  this  mem- 
brane in  its  entirety  is 
known  as  Tomes'  gran- 
ular layer. 

The  cementum  is 
merely  a  periosteal 
growth  of  bone  originat- 
ing in  the  tissue  of  the 
dental  sac  and  adhering 
to  the  dentin.  Although 
at  first  the  enamel  or- 
gan almost  entirely  sur- 
rounds the  dentinal  pa- 
pilla, later  a  portion  of 
that  part  of  it  in  the  re- 
gion of  the  fang  is  ab- 
sorbed in  order  to  allow 
the  cementum  to  reach 
the  surface  of  the  dentin. 

Remains  of  this  regressive  portion  persist  as  the  epithelial  nests  of 
the  dental  root  (compare  p.  216). 

The  contents  of  the  dentinal  papillae  change  into  the  tissue  of  the 
dental  pulp. 

As  early  as  the  third  month  outgrowths  appear  on  the  inner 
side  of  the  enamel  ledge  next  to  the  partly  developed  milk-teeth, 
which  represent  the  anlagen  of  the  enamel  organs  of  the  permanent 
teeth.  Their  further  development  is  similar  to  that  of  the  milk  teeth. 
The  enamel  organs  of  the  molars  are  also  developed  from  an  enamel 
ledge  which  is  practically  a  backward  continuation  of  the  embryonic 
enamel  ledge.  With  their  crowns  presenting,  the  temporary  teeth 


,  © 


i Odontoblasts. 


Fig- >l83- — A  portion  of  a  cross-section  through 
a  developing  tooth  (later  stage  than  in  Fig.  182)  ; 
X  720  :  The  dentin  is  formed,  but  has  become  homo- 
geneous from  calcification.  Bleu  de  Lyon  differen- 
tiates it  into  zones  (a  and  6).  At  c  is  seen  the  in- 
timate relationship  of  the  odontoblasts  to  the  tissue  of 
the  dental  pulp. 


THE  ORAL   CAVITY.  221 

at  last  break  through  the  epithelium  of  the  gums.  When  the  de- 
velopment of  the  permanent  teeth  is  so  far  advanced  that  they  are 
ready  to  perforate,  regressive  processes  begin  at  the  roots  of  the 
milk-teeth,  which  are  due,  as  in  like  conditions  of  the  bone,  to  the 
action  of  certain  cells,  which  are  here  known  as  "  odontoclasts." 
The  crowns  of  the  milk-teeth  are  then  thrown  off,  one  by  one,  by 
the  growing  permanent  teeth. 

For  further  information  as  to  the  teeth  and  their  development,, 
see  the  articles  by  Ebner  (91),  whose  studies  we  have  to  a  great  ex- 
tent followed  on  this  subject. 

2.  THE  TONGUE. 

The    Lingual  Mucous   Membrane  and  its  Papillae. — The 

mucous  membrane  of  the  tongue  differs  in  general  very  little  from 


Fig.  184. — Fungiform  papilla  from  human  tongue. 

that  lining  the  rest  of  the  oral  cavity.  It  must,  however,  be  borne 
in  mind  that  in  the  greater  part  of  the  tongue  the  submucosa  is 
poorly  developed,  and  as  a  consequence  the  mucous  membrane  on 
the  upper  surface  and  base  of  the  tongue  is  scarcely  movable. 
Other  peculiarities  of  the  lingual  mucous  membrane  are  the  absence 
of  glands  in  the  mucosa  on  the  upper  surface  of  the  tongue, — 
although  glands  are  found  in  the  musculature  of  the  tongue,  their 
ducts  passing  through  the  mucosa, — the  presence  of  epithelial 
papillae,  and  of  lymph-follicles  at  the  base  of  the  tongue. 

The  upper  surface  of  the  tongue  is  roughened  by  the  presence 
of  epithelial  projections,  the  lin&tal papilla.     The  latter  are  almost!, 
entirely  epithelial  structures,  and  should  not  be  confused  with  those) 
papillae  which  are  composed  exclusively  of  connective  tissue.     There* 


222 


THE    DIGESTIVE    ORGANS. 


are  several  classes  of  lingual  papillae — the  filiform,  the  fungiform, 
and  the  circumvallate  papillae.  The  most  numerous  are  the  thread- 
like or  filiform  papilla  (from  0.7  to  3  mm.  long).  These  are  scat- 
tered over  the  entire  upper  surface  of  the  tongue,  and  consist  of 
conic  projections  of  the  epithelium  and  of  the  mucosa.  The  con- 
nective-tissue portions  of  these  papillae  are  very  thin  and  long.  The 
basal  layers  of  the  epithelium  can  not  be  distinguished  from  the 
same  layers  covering  the  surrounding  mucosa,  but  the  more  super- 


Papilla  filiformis. 


«rr — Tongue  epithe- 
§KK>        Hum. 


-Connective-tissue 
papilla. 


:-V  .  ":•.  .•;'.'  .;'  •'•': 


•:'  '•'  ''/  !''  ,-  .''" 
,'  '.  •<   A1 ,»'  v     •  •  ; 


^Mr-Mucosa. 


-Basal  epithelial 
layer. 


Fig.  185. — From  a  cross-section  of  the  human  tongue,  showing  short,  thread-like  papillae 

(filiform)  ;   X  140. 

ficial  layers  are  differentiated,  in  that  their  cells  are  arranged  parallel 
to  the  long  axes  of  the  papillae  and  overlap  each  other  like  tiles 
(Fig.  185).  Their  free  ends  are  often  continued  into  several  spine- 
like  processes.  Less  numerous  than  the  filiform  are  the  fungi  form 
papilla  (from  0.7  to  1.8  mm.  in  height)  scattered  here  and  there 
between  the  former.  They  are  nearly  hemispheric  in  shape,  and  are 
joined  to  the  surface  of  the  tongue  by  a  slightly  constricted  base. 
At  times  they  are  even  partly  sunk  into  the  mucous  membrane. 
The  mucosa  is  raised  under  the  epithelium  to  form  connective -tissue 
papillae  (Fig.  184).  On  the  free  surface  of  the  fungiform  papillae 


THE    ORAL   CAVITY. 


223 


are  sometimes  found  taste-buds,  or  taste-goblets,  which  lie  im- 
bedded in  the  epithelium  and  extend  through  its  entire  thickness. 
The  circumvallatt  papilla?  occupy  a  definite  region  on  the  upper 
surface  of  the  tongue,  and  are  arranged  in  two  rows,  forming 
almost  a  right  angle,  with  the  apex  directed  backward  and  situated 
just  in  front  of  the  foramen  caecum  (Morgagni).  These  papillae 
are  few  in  number,  about  eight  to  fifteen  in  all.  In  shape  they 
are  similar  to  those  of  the  fungiform  type,  but  are  much  larger 
(about  I  or  2  mm.  in  diameter),  and  sunk  so  deeply  into  the 
mucous  membrane  that  the  latter  forms  a  wall  around  their  sides. 
Here  also  the  mucosa  passes  up  into  the  papillae  and  forms  con- 
nective-tissue papillae  of  its  own  at  the  upper  surface,  while  at  the 
sides  it  merely  adheres  to  the  smooth  inner  surface  of  the  epithelial 
layer.  Taste-buds  are  found  in  the  epithelium  at  the  sides  of  the 
papillae,  and  also  in  that  of  the  ridges  surrounding  the  papillae.  At 
the  sides  of  the  human  tongue  and  near  its  base  are  the  so-called 
fimbrice  lingua.  These  are  irregular  folds  of  mucous  membrane, 


rt*£ 


Fig.  186. — Longitudinal  section  of  foliate  papilla  of  rabbit,  showing  taste-buds. 

the  sides  of  which  also  contain  taste-buds.  In  the  rabbit  they  are 
more  regular  in  structure  and  consist  of  parallel  folds  of  mucous 
membrane  thickly  dotted  with  taste-buds,  and  are  termed  the  foliate 
papilla.  In  place  of  the  circumvallate  papillae,  the  guinea-pig  pos- 
sesses structures  similar  to  the  foliate  papillae  of  the  rabbit. 

Into  the  depressions  in  which  the  circumvallate  papillae  lie  and 
into  those  between  the  folds  of  the  fimbriae  linguae  open  the  ducts 
of  numerous  serous  glands,  the  glands  of  Ebner  (see  below). 

The  Taste-buds. — The  gustatory  organs  in  the  form  of  taste- 
buds  are  found  on  the  surface  of  the  tongue,  principally  on 
the  lateral  surfaces  of  the  circumvallate  papillae  and  the  fimbriae 
linguae  (foliate  papillae).  They  are  also  occasionally  met  with  in 
the  epithelium  of  the  fungiform  papillae  and  the  soft  palate,  and  on 
the  posterior  surface  of  the  epiglottis.  They  always  lie  imbedded 
in  the  epithelium  and  extend  through  its  entire  thickness  ;  they  are 
ovoid  in  form,  with  base  downward  and  the  smaller  pole  at  the 


224 


THE    DIGESTIVE    ORGANS. 


surface.  The  whole  structure  is  surrounded  by  the  epithelium  of 
the  mucous  membrane  of  the  regions  in  which  they  occur,  except 
at  the  attenuated  outer  end  of  the  taste -bud,  where,  by  means  of  a 
small  opening,  the  taste-pore,  it  communicates  with  the  oral  cav- 
ity. Most  of  the  cells  constituting  the  taste-buds  are  elongated, 
spindle-shaped  structures,  extending  from  one  end  of  the  organ  to 
the  other,  with  spaces  between  them.  There  are  four  varieties  of 
these  cells  :  (i)  The  outer  sustentacular  or  tegmental  cells,  lying  at 
the  periphery  of  the  organ  with  a  nucleus  in  their  center,  and 
having  a  short,  cone-shaped  cuticular  projection  ;  (2)  the  inner 
sustentacular  or  rod-shaped  cells,  which  are  more  slender  structures 
with  basally  situated  nuclei  and  without  a  cuticular  projection  ; 
between  the  latter  are  (3)  elongated,  spindle-shaped,  neuro-epithe- 


Epithelium.  "* 


Taste-buds.   " 


Groove  sur- 
rounding 
papilla. 


Ebner's 

gland. 


Fig.  187. — Longitudinal  section  of  a  human  circumvallate  papilla  ;   X  2O- 

lial  cells,  with  the  nucleus  of  each  in  the  thickest  portion  of  the 
cell,  and  with  slender,  stiff  processes  projecting  into  the  taste-pore  ; 
(4)  a  few  broad  basal  cells,  communicating  with  each  other  as  well 
as  with  the  sustentacular  cells  by  numerous  processes.  We  have, 
therefore,  in  the  cells  of  the  first,  second,  and  probably  fourth 
varieties,  elements  which  belong  exclusively  to  the  sustentacular 
apparatus  of  the  organ  (Hermann,  85,  88). 

Von  Ebner  found  in  the  taste-buds  of  the  circumvallate  papillae 
of  man,  monkey,  and  cat,  as  well  as  of  the  papillae  foliatae  of  the 
rabbit,  an  open  space  situated  between  the  taste-pore  and  the  tip 
of  the  taste-bud  (Fig.  188).  These  spaces  vary  according  to  the 
species,  and  are  bounded  above  by  the  summits  of  the  tegmental 
cells  and  laterally  and  below  by  the  more  centrally  situated  sus- 


THE    ORAL   CAVITY. 


225 


tentacular  cells.  The  cavities  are  often  10  /JL  in  depth,  and  are 
filled  with  a  fluid  apparently  in  communication  with  the  fluid  of 
the  depression  into  which  the  circumvallate  papillae  are  sunk.  The 
processes  of  the  neuro-epithelial  cells  project  into  the  cavity  from 
its  floor  and  lateral  walls,  but  do  not  extend  as  far  as  the  taste- 
pore. 

The  circumvallate  papillae  are  differentiated  from  the  adjacent 
surface  of  the  tongue  by  the  development  of  a  solid  encircling 
epithelial  ridge.  Nu- 
merous taste-buds  ap- 
pear on  the  surface 
quite  early  in  the  his- 
tory of  the  embryo. 
These,  however,  dis- 
appear completely 
when  the  permanent 
taste  -  buds  develop 
from  the  basal  cells 
of  the  epithelial  ridge. 
Similar  phenomena 
occur  in  the  fungiform 
papillae  (  Hermann, 


Process  of 
neuro-epi 

Epithe-    Nerve-          thelial      Taste- 
lium.       fibrils. 


cell. 


pore. 


Neuro-epithe- 


B." 


Sustentacular 
cell. 


Terminal 

I branches  of 

nerves. 


' JJ W>  &>•    ^*-^    " 

Fig.  1 88. — Schematic   representation    of   a  taste-goblet 
(partly  after  Hermann,  88). 


The  neural  epith- 
elia  of  the  taste-gob- 
lets were  formerly  re- 
garded as  directly 
connected  with  the 

nerve-fibers  by  means  of  long  processes,  but  the  latest  researches 
have  shown  that  dendrites  of  sensory  neurones  (sensory  nerves) 
enter  the  taste-buds  and  end  free  in  telodendria.  The  latter  sur- 
round the  neuro-epithelial  and,  to  some  extent,  the  sustentacular 
cells,  their  relations  depending  upon  contact. 

The  Lymph-follicles  of  the  Tongue  (Folliculi  linguales) 
and  the  Tonsils. — At  the  root  of  the  tongue,  and  especially  at  its 
sides,  are  numerous  elevations  due  to  the  increased  quantity  of 
lymphoid  tissue  found  in  the  mucosa  of  these  regions,  the  lingual 
tonsils,  or  lingual  follicles.  In  the  center  of  each  follicle  is  a  cavity 
communicating  with  the  exterior  and  caused  by  an  invagination  of 
the  epithelium.  The  lymphoid  tissue  contains  a  number  of  more  or 
less  distinctly  defined  lymph-nodules,  some  even  showing  germ 
centers  (vid.  p.  178).  The  whole  structure  is  surrounded  by  a 
connective-tissue  capsule.  The  epithelial  walls  of  the  follicular 
cavities  often  show  extensive  degenerative  changes,  which  are 
accompanied  by  increased  migration  of  leucocytes  into  the  oral 
cavity.  These  leucocytes  change  (according  to  Stohr,  84)  into  the 
so-called  mucous  or  salivary  corpuscles  of  the  saliva.  The  pharyn- 
geal  tonsils  may  be  regarded  as  clusters  of  small  lymph-follicles, 
15 


226 


THE    DIGESTIVE    ORGANS. 


similar  to  those  found  in  the  tongue.  They  are  covered  by  a 
stratified  pavement  epithelium,  resting  on  a  mucosa  possessing 
papillae  folded  to  form  pits  or  crypts  of  irregular  shape.  The 
adenoid  tissue  of  the  tonsil  is  found  in  the  form  of  diffuse  ade- 
noid tissue  and  a  varying  number  of  more  or  less  clearly  defined 
follicles  of  adenoid  tissue  often  showing  germ  centers  of  Flemming. 


Epithelium.1 
Lymph- follicle. . 


Epithelial 
crypt. 


Connective-tis- 
sue capsule.  - 


Fig.  189. — Section  through  tonsil  of  dog ;  X  2O  •'     At  ^  and  at  the  opposite  side  the 
epithelium  is  composed  of  a  very  thin  layer  of  cells. 


Fig.  190. — The  area  designated  by  a  in  the  previous  illustration,  shown  by  a  higher 
magnification;  X 'about  150:  a,  Leucocytes  in  the  epithelium;  b,  one  of  the  spaces 
in  the  epithelium  filled  with  leucocytes  and  more  or  less  changed  epithelial  cells  ;  c, 
blood-vessel ;  d,  normal  epithelium  ;  e,  basal  cell  of  the  same. 


The  epithelium  lining  the  crypts  or  cavities  of  the  tonsils  shows,  as 
in  the  lingual  follicles,  extensive  degenerative  changes,  resulting 
mainly  in  the  formation  of  variously  shaped,  communicating  spaces 
filled  with  lymphocytes  and  leucocytes.  (See  Fig.  190.) 

Besides  the  nerves  terminating  in  the  taste-buds,  the  tongue  is 


THE   ORAL   CAVITY. 


227 


richly  supplied  with  sensory  nerves  which  terminate  in  free  sen- 
sory endings,  which  may  be  traced  into  the  epithelium,  and  which 
are  especially  numerous  in  the  fungiform  and  circumvallate  papillae  ; 
or  in  smaller  or  larger  end-bulbs  of  Krause  found  in  the  mucosa  of 
the  fungiform  papillae.  The  motor  nerves  of  the  tongue  terminate 
in  motor-endings. 


GLANDS  OF  THE  ORAL  CAVITY. 

The  glands  of  the  oral  cavity  comprise  numerous  lobular, 
tubulo-acinous  glands  situated  in  the  mucosa  and  submucosa  of  the 
lips,  cheeks,  and  tongue,  and  three 
pairs  of  lobar,  tubulo-acinous 
glands  —  the  parotid,  submaxil- 
lary,andsublingual  glands.  These 
are  classified  according  to  their 
secretions  into  those  secreting 
principally  mucus  (human  sublin- 
gual  and  many  of  the  smaller  oral 
glands),  and  known  as  mucous 
glands  ;  those  secreting  a  fluid  al- 
buminoid substance  containing  no 
mucus,  the  serous  glands  (parotid 
glands  and  the  small  glands  near 
the  circumvallate  papillae) ;  and 
those  having  a  mixed  secretion, 
mucous  and  serous  glands  (human 
submaxillary).  The  ducts  of  all 
these  glands  open  into  the  cavity 
of  the  mouth.  The  ducts  of  the 
smaller  oral  glands  are,  as  a  rule, 
short  and  pass  up  through  the 
mucosa  and  the  epithelium  to  open 
on  the  free  surface.  The  principal 
excretory  ducts  of  the  salivary 
glands  are  Steno's  ducts (Stenson's 
ducts),  passing  from  the  parotid  glands  to  the  mouth  ;  Wharton's 
ducts,  the  ducts  of  the  submaxillary  glands,  and  Bartholin's  ducts 
for  the  sublingual  glands.  The  salivary  glands  consist  of  numerous 
lobules  and  small  lobes  of  glandular  tissue,  surrounded  by  a  thin 
fibrous-tissue  capsule  which  sends  septa  and  trabeculae  between  the 
lobules  and  lobes.  The  duct  of  each  gland  on  reaching  the  gland 
divides  into  smaller  ducts,  which  penetrate  the  gland  between  the 
lobes,  the  interlobar  ducts  ;  these  in  turn  divide  into  ducts  of  the  next 
order,  which  pass  between  the  lobules,  the  interlobular  ducts.  The 
interlobular  ducts  pass  over  into  short  cylindric  tubes  which  enter 
the  lobules,  and  are  known  as  intralobular  ducts.  These  are  followed 
by  very  short,  narrow  tubules,  the  intermediate  ducts  or  tubules, 


Fig.  191. — Scheme  of  a  salivary  gland. 


228  THE    DIGESTIVE    ORGANS. 

which  finally  terminate  in  the  alveoli  or  acini,  irregular  and  some- 
what tortuous  tubular  structures  with  a  lumen  and  possessing  an 
epithelium  characteristic  of  the  particular  variety  of  the  gland  (see 
below).  The  epithelium  lining  the  different  portions  of  the  large 
excretory  ducts  varies  somewhat.  For  a  short  distance  from  their 
oral  end  they  are  lined  by  a  stratified  columnar  epithelium  con- 
sisting of  two  layers  of  cells  (Wharton's  ducts  are  now  and  then 
lined  for  a  short  distance  by  a  stratified  pavement  epithelium 
continuous  with  that  lining  the  mouth).  Beyond  this  stratified 
columnar  epithelium,  which  extends  for  a  variable  distance,  the 
large  excretory  ducts,  the  interlobar  and  interlobular  ducts  are  lined 
by  a  pseudostratified  columnar  epithelium,  possessing  two  rows  of 
nuclei  (Steiner).  Outside  of  the  epithelial  lining  there  is  found  a 
firm  fibro-elastic  covering,  forming  the  wall  of  the  ducts.  The 
intralobular  ducts  are  lined  by  a  single  layer  of  columnar  cells,  the 
basal  half  of  each  cell  showing  a  distinct  striation.  The  interme- 
diate portions  of  the  ducts  are  lined  by  a  low,  cubic,  or  flattened 
epithelium. 

Between  the  membrana  propria  and  the  secreting  epithelium  of 
the  tube,  and  more  especially  in  the  acini,  are  branched  cells  which 
anastomose  with  each  other,  the  so-called  basket  cells.  Their 
processes  penetrate  between  the  glandular  cells  and  form  a  sup- 
porting structure  for  them.  The  homogeneous  membrana  propria 
surrounding  the  entire  glandular  tube  is  in  close  relationship  to 
these  cells. 

We  shall  now  consider  more  in  detail  the  structure  of  the 
alveoli  or  acini  of  the  salivary  glands. 


SALIVARY  GLANDS, 

The  Parotid  Gland  (Serous  Gland). — The  epithelial  cells  lining 
the  acini  of  this  gland  are  short,  irregularly  columnar  or  cubic 
cells,  their  structure  changing  according  to  their  physiologic  condi- 
tion. When  at  rest  the  secreting  cells  are  only  slightly  granulated 
and  contain  a  large  quantity  of  clear  secretion  (paraplasm),  while 
the  nuclei  are  irregular  and  indented.  As  soon  as  the  protoplasm 
of  the  cells  commences  the  formation  of  secretion,  the  cells  become 
smaller,  more  granular  and  opaque,  and  their  nuclei  assume  a 
spheric  shape  ;  when,  however,  the  cells  throw  off  a  portion  of  the 
granular  material,  an  immediate  increase  in  their  protoplasm  is 
noticed.  After  a  long  period  of  secretion  the  cells  become  still 
smaller  and  their  contents  still  more  turbid.  They  now  contain 
very  little  protoplasm.  These  phenomena  can  only  be  regarded  as 
due  to  the  fact  that  the  granular  paraplasm  is  formed  at  the  expense 
of  the  protoplasm  of  the  cell  during  the  period  of  rest. 

The  Sublingual  Gland  (Mucous  Gland). — In  the  acini  of 
mucous  glands  there  are  found  two  varieties  of  cells:  (i)  True 
mucous  cells,  which,  when  filled  with  secretion,  are  large  and 


SALIVARY   GLANDS. 


229 


clear,  with  their  nuclei  always  at  the  periphery.  During  the  ex- 
pulsion of  the  secretion  the  mucous  cells  decrease  in  size  and 
become  cloudy,  while  the  nuclei  leave  the  periphery  and  increase 
in  size.  (2)  Cells  rich  in  protoplasm,  situated  in  close  apposition 
to  the  membrana  propria.  These  cells  resemble  in  structure  serous 
cells,  and  are  found  either  singly  or  in  groups  of  crescentic  shape. 
They  are  known  as  the  crescents  of  Gianuzzi  or  the  demilunes  of 
Hcidenhain.  The  margins  of  the  individual  cells  composing  the 
crescents  are  often  so  faintly  outlined  that  the  whole  structure  has 
the  appearance  of  a  large  polynuclear  giant  cell. 


Acini. 


Fig.  192. — Section  through  salivary  gland  of  rabbit,  with  injected  blood-vessels;   X  7°- 


The  demilunar  cells  have  been  variously  interpreted  by  different 
observers.  They  have  been  regarded  as  permanent  cells  with  a 
special  secretion,  as  transitional  structures,  and  again  as  cells  des- 
tined to  replace  the  degenerated  mucous  cells.  Stohr  (87)  be- 
lieves that  the  cells  of  the  acini  are  never  destroyed  in  the  process 
of  mucous  secretion,  and  that  the  crescents  of  Gianuzzi  are  there- 
fore merely  a  complex  of  cells  containing  no  secretion,  which  have 
been  crowded  to  the  wall  by  the  adjacent  enlarged  and  distended 
cells.  Solger  (96),  on  the  other  hand,  does  not  regard  the  demi- 
lunes as  transitional  structures  whose  function  is  to  replace  the 


230 


THE    DIGESTIVE    ORGANS. 


destroyed  cells,  but  considers  them  to  be  permanent  secreting  cells 
— an  opinion  which  he  bases  on  the  results  of  special  methods  of 
investigation.  According  to  him,  then,  the  mucous  salivary  glands 
are  mixed  glands,  in  that  the  demilunes  consist  of  cells  of  a  serous 
type,  while  the  remaining  elements  are  mucous  in  character.  The 
destruction  of  mucous  cells  during  secretion  is  not  admitted  by  him 


Connective 
tissue. 


Gland    cell 
of  acinus. 


Intralobu- 
lar  duct. 


Intermedi- 
ate duct. 


Fig.  193. — Section  from  parotid  gland  of  man. 

(compare  also  R.  Krause).     This  latter  view  seems  more  in  accord 
with  recent  observations. 

The  Submaxillary  Gland  (Mixed  Gland). — With  regard  to 
the  mixed  glands  it  is  sufficient  to  say  that  there  is  a  simultaneous 
secretion  of  serous  and  mucous  fluids,  and  that  these  two  sub- 
stances are  produced  in  separate  but  adjacent  acini,  of  which  the 


Crescents  of 
Gianuzzi. 


Fig.  194.— From  section  of  human  sublingual  gland. 


one  type  possesses  a  structure   identical  with  that   found   in  the 
parotid  and  the  other  with  that  in  the  sublingual. 

By  means  of  various  methods  the  existence  of  a  network  of 
tubules  surrounding  the  glandular  cells  may  be  demonstrated  both 
in  the  serous  and  mucous  glands.  The  same  arrangement  may  be 


SALIVARY  GLANDS.  23  I 

observed  in  the  case  of  the  cells  forming  the  demilunes.  The 
course  of  these  tubules  may  be  followed  to  their  junction  with  the 
lumen  of  the  secreting  portion  of  the  gland  tubule,  and  the  whole 
structure  would  seem  to  indicate  that  the  entire  surface  of  the  cells 
is  concerned  in  the  act  of  secretion  (Erik  Miiller,  95  ;  Stohr, 

96,  ii). 

As  to  the  part  that  the  intermediate  tubules  and  the  intralobular 
tubes  play  in  the  process  of  secretion,  Merkel's  (83)  theory  is  of 
interest.  He  believes  that  the 
former  yield  a  part  of  the  water 
in  the  saliva,  while  the  salts  are 
furnished  by  the  rod  -  shaped 
epithelium  of  the  intralobular 
tubes.  These  views  of  Merkel 
have  been  questioned,  as  it  has 
been  shown  by  chemic  analysis 
that  the  relative  quantity  of 
water  and  salts  in  the  secretion 
of  the  salivary  glands  is  not  at 
all  proportionate  to  the  number 
of  the  intermediate  tubules  and 

inrralohiilar  ruH^c         For  <-vam  Fig-  X95- — A  number  of  alveoli  from  the 

exam-     submaxillary  gland  of  dog)  stained  in  chrome. 

pie,  Werther  finds  that  although       silver,  showing  some  of  the  fine  intercellular 

a  great  many  intermediate  tu-     tubules, 
bules    are    present  in  the  par- 
otid gland  of  the  rabbit  and  none  at  all  in  the  submaxillary  gland 
of  the  dog,  nevertheless  the  secretions  of  these  glands  contain  equal 
quantities  of  water.      Furthermore,  the  secretions  of  the  parotid  of 
the  rabbit  and  of  the  sublingual  of  the  dog  show  equal  quantities  of 
salts,  in  spite  of  the  fact  that  in  the  former  there  are  large  numbers 
of  intralobular  tubes  with  rod-shaped  epithelium  and  in  the  latter 
none  at  all. 

THE  SMALL  GLANDS  OF  THE  MOUTH. 

Besides  the  larger  glands,  there  are  in  the  oral  cavity  numerous 
small  lobular,  tubulo-acinous  and  simple  branched  tubulo-acinous 
glands.  They  are  mostly  of  the  mixed  type,  and  are  called,  accord- 
ing to  their  location,  glandulae  labiales,  palatinae  and  linguales. 
Serous  glands,  known  as  v.  Ebner's  glands,  occur  in  the  tongue, 
their  ducts  opening  into  the  depressions  of  the  circumvallate  and 
foliate  papillae.  The  absence  of  intralobular  tubes  and  well-defined 
intermediate  tubules  is  characteristic  of  all  the  smaller  glands  of  the 
oral  cavity.  As  a  consequence  the  secreting  tubules  are  composed 
almost  entirely  of  those  parts  corresponding  to  the  acini  of  the 
larger  glands. ,  It  appears  that  the  smaller  mucous  glands,  except 
those  of  the  lips  (J.  Nadler),  do  not,  as  a  rule,  contain  typical 
demilunes. 

The  salivary  glands  and  smaller  glands  of  the  mouth  have  a 


232  THE    DIGESTIVE    ORGANS. 

rich  blood  supply.  In  the  salivary  glands  the  arteries  follow  the 
ducts  through  their  repeated  branching,  ultimately  ending  in  capil- 
laries which  form  a  network  inclosing  the  acini  and  the  terminal 
portions  of  the  system  of  ducts. 

The  lymphatics  begin  in  clefts  in  the  connective  tissue  surround- 
ing and  separating  the  acini.  Larger  lymph-vessels  are  found  in 
the  connective  tissue  separating  the  lobules  and  lobes  of  the  gland. 

The  nerve  supply  of  the  salivary  glands,  may,  owing  to  the  im- 
portance of  these  structures,  receive  somewhat  fuller  consideration. 
Their  nerve  supply  is  from  several  sources.  That  of  the  sublin- 
gual  and  submaxillary  glands  will  be  considered  first.  Sensory 
nerve-fibers  (no  doubt  the  dendrites  of  sensory  neurones,  the  cell- 
bodies  of  which  are  situated  in  the  geniculate  ganglion)  terminate  in 
free  sensory  endings  in  the  large  excretory  ducts  and  their  branches. 
These  medullated  fibers  accompany  the  ducts  in  the  form  of  small 
bundles.  From  place  to  place  one  or  several  fibers  leave  these 
bundles  and,  after  dividing  a  number  of  times,  lose  their  medullary 
sheaths.  After  further  division  the  nonmedullated  branches  form 
plexuses  under  the  epithelial  lining  of  the  ducts.  From  the  fibers 
of  these  plexuses  terminal  fibrils  are  given  off,  which  enter  the 
epithelium,  to  end,  often  near  the  free  surface,  on  the  epithelial  cells 
(Arnstein,  95;  Huber,  96).  The  secretory  cells  of  the  acini  receive 
their  innervation  from  sympathetic  neurones.  The  cell-bodies  of 
those  supplying  the  sublingual  glands  are  grouped  in  a  number  of 
small,  sympathetic  ganglia  situated  in  a  small  triangle  formed  by  the 
lingual  nerve,  the  chorda  tympani  and  Wharton's  duct,  the  chorda- 
lingual  triangle.  These  ganglia  may  be  known  as  the  sublingual 
ganglia  (Langley).  The  cell-bodies  of  the  sympathetic  neurones 
supplying  the  secretory  cells  of  the  submaxillary  glands  are  grouped 
in  small  ganglia  situated  on  Wharton's  duct  just  before  it  enters  the 
gland,  in  the  hilum  of  the  gland,  and  on  the  interlobar  and  inter- 
lobular  ducts  ;  they  may  be  spoken  of  collectively  as  the  submax- 
illary ganglia.  In  the  glands  under  discussion,  the  neuraxes  of  the 
sympathetic  neurones  are  grouped  to  form  small  bundles,  which 
divide  repeatedly,  the  resulting  divisions  joining  to  form  plexuses 
situated  in  the  outer  portion  of  the  walls  of  the  ducts,  and  as  such 
may  be  followed  along  the  ducts,  the  bundles  of  nerve-fibers  be- 
coming smaller  and  the  division  of  the  bundles  of  fibers  and  the 
individual  fibers  occurring  oftener  as  the  smaller  divisions  of  the 
system  of  ducts  are  reached.  On  reaching  the  acini,  the  terminal 
branches  of  the  nerve  -fibers  form  a  plexus  outside  of  the  basement 
membrane,  epilamellar  plexus  ;  from  this  branches  are  given  off 
which  penetrate  the  basement  membrane,  some  forming  ^hypolam- 
ellar plexus,  others  ending  on  the  gland-cells  in  small  granules  or 
clusters  of  granules  (Arnstein).  Throughout  their  entire  course  the 
neuraxes  of  the  sympathetic  neurones  are  varicose,  nonmedullated 
nerve-fibers.  The  nerve-fibers  of  the  chorda  tympani  end  in  ter- 
minal end-baskets,  inclosing  the  cell-bodies  of  the  sympathetic 


THE    PHARYNX    AND    ESOPHAGUS.  233 

neurones  found  in  the  sublingual  and  submaxillary  ganglia,  and  not 
in  the  glands,  as  generally  stated  by  writers.  The  increase  of  secre- 
tion from  the  submaxillary  and  sublingual  glands  on  direct  or  indi- 
rect stimulation  of  the  chorda  tympani  is  due,  therefore,  not  to  a 
direct  stimulation  of  the  gland-cells  by  the  fibers  of  this  nerve,  but 
to  a  stimulation  of  the  sympathetic  neurones  of  the  sublingual  and 
submaxillary  ganglia,  the  neuraxes  of  which  convey  the  impulse  to 
the  gland-cells.  These  glands  have  a  further  nerve  supply  from  the 
superior  cervical  ganglia  of  the  cervical  sympathetic.  The  neuraxes 
of  sympathetic  neurones,  the  cell-bodies  of  which  are  situated  in  the 
superior  cervical  ganglia,  accompany  the  blood-vessels  to  the  sub- 
lingual  and  submaxillary  glands  ;  their  mode  of  termination  is, 
however,  not  as  yet  determined.  The  cell-bodies  of  the  sympathetic 
neurones  here  in  question  are  surrounded  by  end-baskets  of  nerves 
which  leave  the  spinal  cord  through  the  second,  third,  and  fourth 
dorsal  spinal  roots.  The  blood-vessels  of  the  salivary  glands  are 
also  richly  supplied  with  vasomotor  nerves,  the  neuraxes  of  sympa- 
thetic neurones,  which  terminate  on  the  muscle-cells  of  their  walls. 
The  nerve  supply  of  the  parotid  glands  is,  in  the  main,  like  that  of 
the  other  salivary  glands  here  described,  although  it  has  not  been 
worked  out  with  the  same  detail.  The  cell-bodies  of  the  sympathetic 
neurones,  the  neuraxes  of  which  innervate  the  gland-cells,  are,  it 
would  appear,  situated  in  the  otic  ganglia.  The  nerve-ending  in 
the  smaller  glands  of  the  mouth  is  similar  to  that  given  for  the 
salivary  glands,  as  has  been  shown  by  Retzius  and  other  observers. 
It  is  very  probable  that  the  cell-bodies  of  the  sympathetic  neu- 
rones, the  neuraxes  of  which  innervate  the  glands  of  the  tongue,  are 
situated  in  the  small  sympathetic  ganglia  found  on  the  lingual 
branches  of  the  glossopharyngeal  and  lingual  nerves. 


B.  THE  PHARYNX  AND  ESOPHAGUS. 

The  mucous  membrane  of  the  pharynx  and  esophagus  is  similar 
in  structure  to  that  of  the  oral  cavity. 

The  epithelium  is  of  the  stratified  squamous  variety,  and  also 
contains  prickle  cells  and  keratohyalin.  (See  Skin.)  A  stratified 
ciliated  epithelium  is  present  only  in  the  fornix  in  the  region  of  the 
posterior  nares.  The  area  covered  by  this  type  of  epithelium  is 
more  extensive  in  the  fetus  and  new-born,  and  extends  over  the 
whole  nasopharyngeal  vault.  In  the  human  embryo  the  superficial 
epithelial  cells  of  the  esophagus  possess  cilia  up  to  the  thirty- 
second  week  (Neumann,  76).  The  papillae  of  the  mucosa  are 
loosely  arranged  and  are  in  the  form  of  slender  cones.  The 
mucosa  of  the  pharynx  contains  diffuse  adenoid  tissue  rich  in  cells 
which  in  some  places  forms  accessory  tonsils  (yid.  p.  225).  There 
are  but  few  mucous  glands  in  the  submucous  tissue  of  the  esoph- 
agus, but  when  present  they  contain  well-marked  demilunes.  In 


234 


THE    DIGESTIVE    ORGANS. 


man  the  ducts  of  these  glands  do  not  reach  the  surface  between 
the  connective-tissue  papillae,  as  in  the  external  skin,  but  pass  up 
through  them  into  the  epithelium  and  thus  to  the  surface.  A  layer 
consisting  of  nonstriated  muscle-fibers,  the  muscularis  mucosa,  the 
majority  of  the  cells  of  which  show  a  longitudinal  arrangement,  is 
found  between  the  mucosa  and  submucosa  in  the  esophagus,  but 
not  in  the  pharynx. 

The  external  muscular  coat  of  the  pharynx  is  made  up  of 
transversely  striated  muscle-fibers,  arranged  in  a  complicated  man- 
ner. This  tissue  extends  downward  to  about  the  middle  of  the 


.--   Epithelium. 


^ Mucosa. 


Muscularis 
mucosae. 


•:• Submucosa. 


Circular  layer 
of  muscle. 


<•--  Longitudinal 
muscle  layer. 


_  Outer  connec- 
-  tissue 


Jtive  -  Us 
coat. 


Fig.  196. — Section  of  esophagus  of  dog  ;   X 


esophagus,  in  which  it  consists  of  an  outer  longitudinal  and  an  inner 
circular  layer.  In  the  lower  half  of  the  esophagus  nonstriated 
muscle-fibers  alone  are  present.  There  is  no  sharply  defined  line 
of  demarcation  between  the  two  types  of  muscular  tissue,  as  the 
fibers  of  the  unstriped  variety  penetrate  for  some  distance  upward 
into  the  substance  of  the  striated  muscle,  giving  the  tissue  here  a 
mixed  character. 


THE    STOMACH    AND    INTESTINE. 


235 


C  THE  STOMACH  AND  INTESTINE. 

J.  GENERAL  STRUCTURE  OF  THE  INTESTINAL  MUCOUS 
MEMBRANE. 

The  mucous  membrane  of  the  stomach  and  intestine,  unlike 
that  of  the  esophagus  and  oral  cavity,  possesses  an  epithelium  of 
the  simple  columnar  variety  with  elongated  cells  (about  22  //  in 


Basal  epi- 
thelial 
cells. 

Gland- 
cells. 


-    Lumen. 


Branched 
papilla 
of  mu- 
cosa. 


Fjg.  ioj[. — Part  of  section  of  human  esophagus,  showing  duct  of  mucous  gland  ;  X  I2°- 

height).  In  the  intestine  the  epithelium  shows  a  well-marked 
striated  cuticular  border,  striated  protoplasm  in  the  outer  ends  of 
the  cells,  extending  to  the  immediate  vicinity  of  the  nuclei,  which 
are  situated  in  the  basal  portions  of  the  cells.  The  basal  portion  of 
each  cell  consists  of  nonstriated  protoplasm,  ending  in  a  longer  or 
shorter  process  which  extends  to  the  basement  membrane,  or  possibly 


236  THE    DIGESTIVE    ORGANS. 

even  penetrates  it.  The  epithelial  cells  have  the  power  of  produc- 
ing mucus,  a  phenomenon  which,  in  the  normal  condition,  rarely 
embraces  whole  areas  of  epithelium  ;  these  cells  (goblet  cells)  are 
usually  surrounded  by  others  which  are  unchanged  (for  details  about 
goblet  cells  see  General  Histology,  p.  81).  Throughout  the  entire 
intestinal  tract  the  epithelium  forms  simple,  branched,  and  compound 
tubular  and  alveolar  glands.  These  are  depressions  lying  in  the 
mucosa,  and  only  in  the  duodenum  extend  beyond  it  into  the  sub- 
mucosa. 

The  mucosa  consists  of  adenoid  tissue,  containing  relatively 
few  cells.  It  fills  the  interstices  between  the  glands,  and  often  forms 
a  thin  but  continuous  layer  (granular  layer  of  F.  P.  Mall)  below  the 
glands.  It  is  therefore  obvious  that  the  development  of  the 
mucosa  is  inversely  proportionate  to  the  number  and  the  density  of 
arrangement  of  the  glands ;  when  the  latter  are  present  in  large 
numbers,  as,  for  instance,  in  the  stomach,  the  mucosa  is  reduced  to 
a  minimum.  In  the  small  intestine  it  forms  not  only  the  perma- 
nent folds,  but  also  certain  finger-like  elevations  known  as  villi,  which 
are  covered  with  epithelium  and  project  into  the  lumen  of  the  intes- 
tine, thus  increasing  to  a  considerable  extent  the  surface  area  of  the 
mucous  membrane.  In  the  mucosa  are  found  small  nodules  of 
adenoid  tissue.  These  are  spoken  of  as  lenticular  glands  when 
occurring  in  the  stomach,  as  solitary  glands  when  found  in  the 
upper  portion  of  the  small  intestine  and  in  the  large  intestine.  In 
the  lower  portion  of  the  small  intestine  they  are  grouped  to  form  the 
agminated  glands,  or  Peyer's  patches,  which,  when  large,  extend 
into  the  submucosa.  Beneath  the  stratum  proprium  is  a  layer 
consisting  of  two  or  three  strata  of  unstriped  muscle- fibers,  the 
muscularis  mucosce.  As  a  rule,  it  is  composed  of  an  inner  circular 
and  an  outer  longitudinal  layer.  This  arrangement  is  interrupted 
only  where  the  larger  glands  and  follicles  penetrate  into  the  sub- 
mucosa. The  epithelium  with  the  glands,  the  mucosa  with  its 
lymph-nodules,  and  the  muscularis  mucosse  form  together  the 
mucous  membrane ',  or  tunica  mucosa. 

Below  the  mucous  membrane  is  the  connective-tissue  subvmcosa. 
This  is  characterized  by  its  loose  structure,  and  consequently  affords 
considerable  mobility  to  the  mucous  membrane.  In  the  small  intes- 
tine it  forms  a  large  number  of  permanent  transverse  folds  known 
as  valvulcg  conniventes  (Kerkring).  In  the  submucosa  of  the 
duodenum  occur  the  secreting  portions  of  Brunncr' s  glands  (gland- 
ulae  duodenales),  and  in  the  small  intestine  the  larger  lymph-nodes 
and  Peyer's  patches. 

External  to  the  submucosa  is  the  muscular  coat,  which  generally 
consists  of  two  layers  of  unstriped  muscle-tissue.  The  inner  layer 
is  composed  of  circular  fibers  (stratum  circulare)  ;  the  outer  layer,  of 
longitudinal  fibers  (stratum  longitudinale).  In  the  colon  the  longi- 
tudinal layer  forms  definite  bands,  the  tanice  coli.  In  some  regions 
the  circular  fibers  are  also  considerably  reinforced,  particularly  in 


THE    STOMACH    AND    INTESTINE.  237 

the  plica  signwidea  which  lie  between  the  taeniae  coli.  At  these 
points  the  longitudinal  layer  also  is  thickened.  In  the  rectum  the 
circular  fibers  form  the  internal  sphincter  ani  muscle.  In  the 
stomach  a  third  layer  is  added  to  the  two  already  mentioned,  with 
fibers  running  obliquely.  It  lies  internal  to  the  circular  fibers,  but 
does  not  form  a  continuous  layer. 

According  to  Legge,  elastic  fibers  are  present  throughout  the 
entire  digestive  tract  of  all  adult  mammalia  and  vary  only  in  minor 
details  in  the  different  species.  In  regions  in  which  the  tunica  mus- 
cularis  is  prominent  the  elastic  fibers  attain  a  considerable  size. 
There  is  also  a  difference  in  their  development  in  carnivora  and 
herbivora.  In  general,  they  form  a  dense  network,  present  not  only 
in  the  serous  layer,  but  also  in  the  submucosa  and  beneath  the 
epithelium.  These  fibers  preserve  the  elasticity  of  the  intestinal 
walls  and  resist  any  hyperextension  of  the  glands  and  follicles. 

The  intestine  is  covered  externally  by  the  peritoneum,  forming 
the  serous  coat,  which  consists  of  an  inner,  very  thin  connective- 
tissue  layer  (subserosa)  and  an  outer  layer  of  mesothelial  cells. 

2.  THE  STOMACH. 

The  general  structure  of  the  gastric  mucous  membrane  is  essen- 
tially the  same  as  that  of  the  intestinal  canal.  It  presents,  however, 
depressions  known  as  gastric 
crypts,  due  to  an  infolding  of  the 
epithelium  into  which  the  gastric  / 

glands  open.      In  the  fundus  the  /---  ^K Epithelial 

crypts    attain   a    depth   of   from  'p 

one-fifth  to  one-sixth  the  thick-  li '  wll^H  & 

ness  of  the  mucous  membrane. 

In  the  pylorus  they  are  deeper,  • 

many  of    them   here   extending 
through  half  the  mucous  mem- 
brane and  some  even   reaching  \Muc.»sa. 
the   muscularis    mucosae.      The 
epithelium    of    the    crypts    and 

that   of  the    folds    between    them  Fig.  198.— Epithelium  of  human  stom- 

is      composed     of    long,     slender       ach»  covering  the  fold  of  mucosa  between 

cells,  with  basally  situated  nu-  £°  gastric  crypts ;  X7oa  Technic  No' 
clei.  That  portion  of  the  cell- 
body  near  its  free  margin  contains  very  little  protoplasm,  but  is,  on 
the  other  hand,  rich  in  paraplasm  ;  the  region  of  the  cell  containing 
the  nucleus  possesses  more  protoplasm.  This  part  of  the  cell 
extends  downward  in  a  curved  process  of  diminishing  size,  which 
assumes  a  position  parallel  to  the  corresponding  parts  of  the  neigh- 
boring cells,  and  finally  penetrates  the  basement  membrane.  Into 
a  single  gastric  crypt  of  the  human  fundus  empty  from  three  to 
seven  gastric  glands.  Each  gland  consists  of  a  simple  tube,  from 


THE    DIGESTIVE    ORGANS. 


0.4  to  2.2  mm.  in  length,  whose  inner  segment,  opening  into  the 
crypt,  is  quite  narrow,  and  is  known  as  the  neck  of  the  gland.  The 
main  portion  of  the  gland  is  called  its  body,  and  the  region  at 
the  distal  blind  end  the  fundus.  In  the  gastric  glands,  more 
especially  in  the  cardia  and  fundus  of  the  stomach,  two  varieties 
of  gland-cells  are  found.  The  cells  of  the  one  variety  lie  against 
the  walls  of  the  gland — that  is,  they  rest  on  its  basement  mem- 
brane— and  are  particularly 
numerous  in  the  neck  and 
body  of  the  gland,  but  not 
so  numerous  in  its  fundus. 
These  are  known  as  the 
parietal,  oxyntic  or  delo- 
morphous  cells  (R.  Heiden- 
hain,  69  ;  Rollet,  70).  Their 
bodies  often  extend  more  or 
less  beyond  the  even  line 


Gastric  crypts 
and  necks 
of  glands. 


Bodies  of  gas- 
tric glands. 


•  Fundus. 


^-'<-:- Mucosa. 


Fig.  199. — From  vertical  section  through 
fundus  of  human  stomach  ;  X  60  :  a  and  b,  Inter- 
lacing fibers  of  the  muscularis  mucosae  ;  from  a 
and  b  muscular  fibers  enter  the  mucosa.  The 
fibers  of  the  layer  b  penetrate  those  of  layer  a. 


Fig.  200. — A  number  of  gastric 
glands  from  the  fundus  of  the  stom- 
ach of  young  dog,  stained  after  the 
chrome-silver  method,  showing  the 
system  of  fine  canals  surrounding 
the  parietal  cells  and  communica- 
ting with  the  lumen  of  the  glands. 


of  the  remaining  cells,  thus  forming,  together  with  the  membrana 
propria,  a  protuberance  (particularly  noticeable  in  the  pig,  where 
almost  the  entire  cell  may  be  enveloped  by  the  basement  membrane, 
giving  it  an  appearance  of  being  entirely  extraglandular).  Toward 
the  lumen  of  the  gland  the  contour  of  these  cells  is  modified  by 
pressure  on  the  part  of  the  adjacent  cells  belonging  to  the  other 
variety,  and  they  are  indented  according  to  the  number  of  the  latter. 


THE    STOMACH    AND    INTESTINE. 


239 


Occasionally,  a  process  is  seen  extending  from  a  parietal  cell  to  the 
lumen  of  the  gland.  The  parietal  cells  are  larger  than  the  cells  of 
the  other  variety  and  richer  in  protoplasm  ;  they  are  of  an  irregular 
oval  or  triangular  shape  and  possess,  as  a  rule,  a  single  nucleus. 

According  to  Erik  Muller  and  Golgi  (93),  there  exists  in  the 
peripheral  protoplasm  of  each  parietal  cell  a  system  of  canals  in 
the  form  of  a  network  communicating  with  the  lumen  of  the  gland 
and  varying  in  structure  according  to  the  physiologic  condition  of 
the  cell — wide-meshed  in  a  state  of  hunger  and  fine-meshed  during 


Epithelium  of 
esophagus. 


Mucous  cardiac 
gland. 


Junction  of 
esophagus 
and  stomach. 

Epithelium    of 
stomach. 

Gastric  crypt. 


Fig.  201.  —  From  a  section  through  the  junction  of  the  human  esophagus  and  cardia  ; 

X5<>. 


digestion.  A  peripheral  zone  differing  from  the  rest  of  the  cell- 
body  may  occasionally  be  demonstrated  in  the  parietal  cells  (mouse) 
by  using  the  method  of  von  Altmann  (vid.  T.  125). 

The  second  variety  of  glandular  cells  is  represented  by  the 
central,  chief,  peptic,  or  adclomorphous  cells.  These  are  short, 
irregular,  columnar  structures  whose  narrower  portions  point  toward 
the  lumen  of  the  gland.  They  are  situated  either  directly  between 
the  lumen  and  the  basement  membrane  of  the  gland,  or  their 


240 


THE    DIGESTIVE    ORGANS. 


Epithelium  ----V- 
of  fold  be-      p 
tween  gas- 
tric crypts. 


basilar  surfaces  border  on  a  delomorphous  cell.  They  are  found 
throughout  the  tubule  of  the  gland  and  occupy  the  spaces  between 
the  delomorphous  cells.  Their  protoplasm  is  dark  and  the  nuclei 
are,  as  a  rule,  somewhat  smaller  than  those  of  the  parietal  cells. 
In  both  varieties  of  cells  mitoses  are  rarely  present  in  man.  In  the 
delomorphous  cells  pluripolar  mitoses  are  sometimes  seen. 

At  the  cardia  the  stratified  squamous  epithelium  of  the  esopha- 
gus terminates  abruptly,  the  basilar  layer  of  this  epithelium  being 
continued  as  the  simple  columnar  epithelium  of  the  stomach. 
(Fig.  20 1.)  In  that  region  of  the  gastric  mucous  membrane  bor- 
dering upon  the  cardia  are  mu- 
cous glands  ( cardiac  mucous 
glands)  similar  in  appearance  to 
those  of  the  esophagus.  The 
crypts  of  this  region  are  not 
supplied  with  true  gastric  glands, 
the  latter  first  making  their  ap- 
pearance at  some  distance  from 
the  cardia  and  increasing  in 
length  toward  the  fundus. 

The  structure  of  the  pyloric 
region  of  the  stomach  differs  in 
some  respects  from  that  of  the 
cardiac  end  and  fundus.  There 
is,  however,  no  sharply  defined 
boundary  between  fundus  and 
pylorus,  but  a  transitional  zone 
in  which  changes  gradually  take 
place.  Toward  the  pylorus  the 
gastric  crypts  gradually  become 
deeper  and  the  parietal  cells  de- 
crease in  number.  Here  also  the 
glands  begin  to  branch.  In  the 
pylorus  itself  the  crypts  fre- 
quently extend  half-way  through 
the  thickness  of  the  mucous 
membrane,  often  even  penetrat- 
ing to  the  muscularis  mucosae, 
in  which  case  the  corresponding 

tubules  become  tortuous  and  arch  over  the  muscularis  mucosae. 
The  most  important  feature  is  that  in  the  great  majority  of  the 
tubules  only  a  single  variety  of  cell  is  present  in  the  pyloric  gland. 
(Only  here  and  there  are  found  parietal  cells  in  the  pyloric  glands 
of  the  human  stomach.)  These  cells  may  be  compared  with  the 
chief  cells  of  the  glands  in  the  fundus.  They  are  columnar,  but 
of  much  more  uniform  structure — a  condition  probably  due  to  the 
general  absence  of  delomorphous  cells.  In  the  immediate  vicinity 
of  the  gastroduodenal  valve  the  pyloric  glands  become  shorter, 


Pyloric 
gland. 


Mucosa.   — 


Muscularis 

mucosae. 


Fig.  202. — From  vertical  section 
through  human  pylorus  ;  X  about  60. 
Technic  No,  241. 


THE    STOMACH    AND    INTESTINE. 


241 


and  other  glands,  which  extend  into  the  submucosa,  and  which 
are  identical  in  structure  with  the  glands  of  Brunner  in  the  duod- 
enum, make  their  appearance.  In  this  portion  of  the  pylorus  are 
also  a  few  scattered  villi,  which  from  their  structure  may  be  con- 
sidered as  belonging  to  the  duodenum  (vid.  Fig.  208). 

In  the  normal  condition  the  mucosa  of  the  stomach  seldom  con- 
tains solitary  lymph-nodules  (lenticular  glands)  in  the  fundus  region, 
but  frequently  in  the  pyloric  region  ;  well-defined  lymph-nodules 
are  constantly  present  in  the  immediate  vicinity  of  the  pylorus. 

The  muscularis  mucosae  is  usually  composed  of  three  layers, 
the  fibers  of  the  individual  layers  forming  distinct  interlacing  bun- 
dles. Individual  muscle-fibers  very  frequently  branch  off  from  the 
inner  layer,  assume  a  vertical  position  and  disappear  among  the 
glands.  This  arrangement  is  especially  well  seen  in  the  muscularis 
mucosae  of  the  fundus  of  the  stomach  (Fig.  199). 

Only  the  inner  and  middle  layers  of  the  muscular  coat  of  the 
stomach  enter  into  the 
formation  of  the  sphinc- 
ter pylori  (Fig.  208). 
The  fibers  of  the  outer 
layer,  however,  pene- 
trate through  the  sphinc- 
ter pylori  and  may  even 
be  traced  into  the  sub- 
mucosa. When  these 
alone  contract,  the  mus- 
cular bundles  of  the 
sphincter  act  somewhat 
as  pulleys,  and  a  mod- 
erate dilatation  of  the 
lumen  of  the  pylorus 
is  the  result  (dilatator 
pylori,  Riidinger,  97 ). 
(For  further  particulars  about  the  stomach,  compare  Oppel,  96.) 

The  changes  which  the  epithelium  and  the  secretory  cells  of  the 
stomach  undergo  during  secretion  are  of  special  importance.  These 
relations  have  been  carefully  studied  in  animals  by  R.  Heidenhain 
(83).  As  far  as  our  present  knowledge  goes,  it  would  seem  that  the 
same  processes  also  occur  in  man.  In  a  state  of  hunger  the  chief 
cells  of  the  fundus  are  large  and  clear,  the  parietal  cells  small  ;  in 
certain  cases  the  parietal  cells  abandon  their  mural  position  and, 
like  the  chief  cells,  border  upon  the  lumen  of  the  gland.  During 
the  first  few  hours  of  digestion  the  chief  cells  remain  large,  but 
become  somewhat  turbid,  while  the  parietal  cells  increase  in  size.  In 
the  dog  from  the  sixth  to  the  ninth  hour  of  digestion,  the  chief 
cells  diminish  in  size  and  become  cloudy,  while  the  parietal  cells  re- 
main large  and  even  increase  in  size.  From  the  fifteenth  hour  on,  the 
process  becomes  reversed  ;  the  chief  cells  enlarge  and  become  clear, 
16 


Mucosa. 


Point  of  di- 
vision   of 
pyloric 
gland. 

Gland-cell. 


P'ig.  203. — From  section  tli rough  human  pylorus  ; 
X  600.     Technic  No.  241. 


242 


THE    DIGESTIVE    ORGANS. 


and  the  parietal  cells  diminish  in  size.  In  a  condition  of  hunger  the 
cells  of  the  pylorus  are  clear,  of  medium  size,  and  do  not  begin  to 
enlarge  until  six  hours  after  feeding.  From  the  fifteenth  hour  on, 
the  cells  become  smaller  and  more  turbid,  while  the  nuclei  return 


Fig.  204. — Section  through  fundus  of  human  stomach  in  a  condition  of  hunger  ;  X  5°°' 

Technic  No.  242. 


Lumen. 


Chief  cell. 


Fig.  205. — Section  through  fundus  of  human  stomach  during  digestion  ;   X  5°°- 

Technic  No.  242. 

to  the  center  of  the  cells.  Since  chemic  examination  has  shown 
that  the  amount  of  pepsin  found  in  the  gastric  mucous  membrane 
increases  with  the  enlargement  of  the  chief  and  pyloric  cells,  and 
decreases  with  their  diminution  in  size,  there  can  be  hardly  any 


THE    STOMACH    AND    INTESTINE.  243 

doubt  that  this  ferment  is  elaborated  by  these  cells.  The  pro- 
cess consists  either  in  a  direct  change  of  the  cellular  protoplasm 
into  the  ferment,  or  in  a  preliminary  stage  before  its  final  trans- 
formation into  the  finished  ferment.  It  is  assumed  that  the  parietal 
cells  secrete  the  acid  of  the  gastric  juice,  although,  in  spite  of  all 
efforts,  it  has  not  yet  been  definitely  proved  that  these  cells  possess 
an  acid  reaction. 

The  vascular  and  lymph-vessels  of  the  stomach,  and  also  its 
nerve  supply,  will  be  considered  in  a  general  discussion  of  these 
structures  pertaining  to  the  entire  intestinal  canal. 


3.  THE  SMALL  INTESTINE. 

The  mucous  membrane  of  the  small  intestine  is  characterized  by 
the  presence  of  villi.  These  are  more  or  less  elongated  elevations 
of  the  mucous  membrane  projecting  into  the  lumen  of  the  intestine. 
They  greatly  increase  the  surface  of  this  portion  of  the  intestine  and 
are  actively  concerned  in  the  absorption  of  its  contents.  The  mu- 
cous membrane  also  forms  permanent  folds  in  both  the  duodenum 
and  the  remainder  of  the  small  intestine,  the  valvulae  conniventes 
(Kerkring).  Upon  these  the  villi  rest,  and,  indeed,  it  is  probable 
that  the  very  existence  of  the  plicae  is  due  to  the  blending  of  the 
basilar  ends  of  the  villi.  The  latter  are  leaf-shaped  in  the  duod- 
enum, columnar  in  the  jejunum,  and  club-shaped  in  the  ileum. 

The  epithelium  of  the  intestinal  mucous  membrane  covers  the 
villi  in  a  continuous  layer,  and  penetrates  into  the  mucosa  to  form 
the  glands.  Its  structure  is  essentially  the  same  in  all  regions  of 
the  small  intestine,  the  cells  being  of  the  high  columnar  variety  with 
free  surfaces  covered  by  wide,  striated  cuticular  borders.  The 
basilar  portions  of  these  cuticular  borders  are  nearly  always  homo- 
geneous, and  upon  vertical  section  give  the  appearance  of  a  fine  line. 
The  cuticular  borders  of  adjacent  cells  blend  with  each  other,  form- 
ing a  continuous  membrane,  large  areas  of  which  may  be  detached 
from  the  villi  (cuticula).  The  body  of  the  cell  consists  of  a  gran- 
ular, reticular,  or  striated  protoplasm,  containing,  especially  at  the 
beginning  of  mucous  secretion,  clear  vacuoles  of  different  sizes — 
mucus.  If  the  cuticular  margin  be  intact,  a  confluence  of  the  vacu- 
oles may  form  a  large  drop  of  mucus.  The  nuclei  lie  usually  in 
the  basilar  third  of  the  cells,  and  only  where  they  show  mitoses,  as 
for  instance  in  the  tubular  intestinal  glands,  do  they  pass  to  the  free 
ends  of  the  cells.  The  basal  ends  of  the  epithelial  cells  in  the  small 
intestine  are  also  seen  to  be  pointed,  and  the  probability  is  that  they 
rest  upon  the  basement  membrane.  The  question  has,  however, 
not  been  fully  settled. 

The  epithelial  cells  undergo  a  special  metamorphosis,  after 
which,  by  an  increased  production  of  mucus,  they  change  into  gob- 
let cells.  From  recent  investigations  it  would  seem  that  any 
epithelial  cell,  whether  it  be  situated  upon  the  upper  surface  of  a 


244 


THE    DIGESTIVE    ORGANS. 


Epithelium 

of  villus. 


villus  or  deep  down  in  one  of  the  tubules  of  the  intestinal  glands,  is 
capable  of  transformation  into  a  goblet  cell.  The  number  of  goblet 
cells  is  subject  to  great  variation  ;  they  are  found  singly  in  small 
numbers,  or  are  very  numerous,  according  to  the  stage  of  digestion 
and  quantity  of  food  in  the  intestine.  The  manner  in  which  an 
ordinary  epithelial  cell  changes  into  a  goblet  cell  is  very  easily 
explained  if  the  mechanical  action  on  the  cell  caused  by  an  accumu- 
lation of  secretion  be  taken  into  consideration.  As  the  secretion 
increases  in  quantity  the  upper  portion  of  the  cell  becomes  distended, 

and  the  remains  of  the 
protoplasm,  together 
with  the  nucleus,  are 
pushed  toward  the  nar- 
row base  of  the  cell  ; 
the  cuticular  zone  is 
stretched,  bulges  into 
the  lumen  of  the  intes- 
tine, and  is  finally  perfor- 
ated, and  perhaps  even 
thrown  off.  In  this  way 
the  cell  loses  its  mucous 
secretion,  collapses,  and 
then  appears  as  a  thin, 
almost  rod  -  like  struc- 
ture, with  a  long  nu- 
cleus. It  is  the  gener- 
ally accepted  theory  that 
such  an  empty  goblet 
cell  may  again  assume 
the  shape  of  an  ordinary 
epithelial  cell  and  repeat 
the  process  just  de- 
scribed. 

Leucocytes  are  some- 
times found  within  the 
epithelial  cells,  but  more 
usually  between  them, 
and  according  to  Stohr 
(84,  89,  94),  when  seen 
in  these  positions,  are 
in  the  act  of  migrating 

into  the  lumen  of  the  intestine.  That  some  of  these  cells  actually 
pass  into  the  lumen  is  probably  true  ;  but  as  yet  no  leucocytes  have 
ever  been  observed  in  the  cuticula  itself,  and  neither  is  the  number 
of  cells  found  in  the  lumen  of  the  intestine  proportionate  to  the  leuco- 
cytes present  in  the  epithelium.  Since  many  are  seen  in  the  epithe- 
lium undergoing  karyokinetic  division,  it  is  more  probable  that  a 
part  of  them  actually  wander  into  the  epithelium  for  the  purpose  of 


Mucosa. 


Muscularis 
mucosse. 


Fig.  206. — Section  through  mucous  membrane 
of  human  small  intestine  ;  X  88.  Technic  No.  243  : 
At  a  is  a  collapsed  chyle-vessel  in  the  axis  of  the 
villus. 


THE   STOMACH    AND    INTESTINE. 


245 


division  (chemotaxis  ?),  only  to  return  to  the  mucosa  after  the  com- 
pletion of  the  process  (compare  p.  54). 

Into  the  spaces  between  the  villi  open  numerous  tubular  glands. 
These  are  seldom  branched,  and  are  known  as  Lieber kukris  glands, 
or  crypts.  Their  length  varies  from  320  fi.  to  450  //.  They  are 
regularly  arranged  in  a  continuous  row,  and  often  have  an  ampulla- 
like  widening  of  their  lumina  extending  almost  to  the  muscularis 
mucosae,  but  never  quite  reaching  it.  They  are  uniformly  distrib- 
uted not  only  throughout  the  small  intestine,  but  also  throughout 
the  large  intestine  and  rectum.  Their  cells  are  somewhat  lower  than 
those  of  the  villi,  and  pos- 
sess a  very  narrow  cuticular 
zone.  The  cells  are,  how- 
ever, conical, — a  condition 
probably  due  to  the  curva- 
ture of  the  glandular  wall, 
— the  base  of  each  cone 
lying  toward  the  basement 
membrane,  the  apex  toward 
the  lumen  of  the  gland — a 
condition  opposite  to  that 
found  in  the  villi.  Numer- 
ous goblet  cells  are  also 
present.  They  vary  only 
slightly  in  shape  during  mu- 
cous secretion,  and  never, 
as  in  the  villi,  assume  the 
form  of  goblets  with  distinct 
pedicles.  Mitoses  are  al- 
ways seen  in  the  intestinal 
glands,  especially  in  cells 
which  do  not  contain  mu- 
cin.  They  are  readily  dis- 
tinguished, since  the  nuclei 
in  process  of  division,  as 
we  have  seen,  lie  outside  of 
the  row  formed  by  the  re- 
maining nuclei.  The  plane 
of  division  in  these  cells  lies 

horizontal  to  the  long  axis  of  the  gland,  so  that  an  increase  in  the 
number  of  cells  results  in  an  increase  in  the  area  of  the  glandular 
walls.  Mitoses  are  very  rarely  observed  in  the  epithelium  covering 
the  villi.  If,  therefore,  any  cells  be  destroyed  on  the  surface  of  the 
villi,  it  must  be  assumed  that  the  loss  is  replaced  by  new  elements 
pushed  up  from  the  glands  below  (Bizzozero,  89,  92,  I). 

The  entire  duodenum,  as  well  as  that  part  of  the  pylorus  in  the 
immediate  vicinity  of  the  pyloric  valve,  is  characterized  by  the 
presence  of  glands  of  a  second  type.  In  the  duodenum  these  are 


Fig.  207. — Longitudinal  section  through  sum- 
mit of  villus  from  human  small  intestine  ;  X  9°° 
(Flemming's  solution)  :  At  a  is  the  tissue  of  the 
villus  axis  ;  l>,  epithelial  cells  ;  c,  goblet  cell ;  </, 
cuticular  zone. 


246  THE    DIGESTIVE    ORGANS. 

seen  intermingled  with  the  glands  of  Lieberkiihn,  and  in  the  pylorus 
with  the  pyloric  glands.  These  glands,  Brunner' s  glands,  have  a 
diameter  of  from  0.5  to  I  mm.,  and  are  compound,  branched  tubu- 
lar glands,  with  tubules  provided  with  alveoli,  especially  along  their 
lower  portions.  The  bodies  of  the  glands  are  situated  principally 
in  the  submucosa,  although  a  part  may  be  in  the  mucosa.  In  the 
stomach  they  open  into  the  gastric  crypts,  in  the  intestine  either  in- 
dependently between  the  villi,  or  into  the  glands  of  Lieberkiihn. 
Here  the  glandular  cells  are  in  general  similar  to  those  of  the  pyloric 
glands,  although,  as  a  rule,  somewhat  smaller  than  the  latter.  Just 
as  the  duodenal  glands  extend  into  the  stomach,  so  also  the  pyloric 
glands  of  the  latter  are  found  in  the  upper  portion  of  the  duodenum. 
Besides  short  villi,  there  are  also  present  in  the  duodenum  depres- 
sions of  the  mucous  membrane  analogous  to  the  gastric  crypts.  The 
glands  of  Lieberkiihn  begin  at  a  certain  distance  from  the  pylorus  ; 
at  first  they  are  short,  and  do  not  attain  their  customary  length  until 
a  point  is  reached  at  which  the  gastric  glands  extending  into  the 
duodenum  finally  disappear  (vid.  Fig.  208).  It  is  therefore  obvious 
that  a  transition  zone  exists  between  pylorus  and  duodenum,  and 
that  a  distinct  boundary  line  can  not  be  drawn  between  the  two,  at 
least  so  far  as  the  mucous  membrane  is  concerned.  The  duodenal 
glands,  as  their  name  would  indicate,  are  present  only  in  the  duod- 
enum. Between  the  jejunum  and  ileum  there  is  no  distinct  boundary, 
not  even  when  microscopically  examined.  The  differences  are  mostly 
of  a  quantitative  nature  ;  in  the  jejunum  the  valvulse  conniventes  are 
more  numerous  than  in  the  ileum,  and  the  villi  more  slender  and 
closer  together.  The  glands  of  Lieberkiihn  also  appear  to  be  more 
numerous  in  the  jejunum. 

The  mucosa  of  the  small  intestine  consists  of  reticular  adenoid 
tissue  containing  lymph-cells.  It  supports  the  glands  and  extends 
into  the  villi  whose  axes  it  forms.  The  mucosa  is  separated  from 
the  glands,  from  the  epithelium  of  the  villi,  as  well  as  from  that  of  the 
remaining  surface  of  the  intestine  by  a  peculiar  basement  membrane. 
The  latter  somewhat  complicates  a  proper  histologic  analysis,  and 
as  a  consequence  opinions  regarding  its  structure  and  significance 
vary  considerably.  By  some  it  has  been  described  as  a  homo- 
geneous, hyaline,  and  exceedingly  fine  membrane  containing  nuclei, 
by  others  as  a  lamella  consisting  entirely  of  endothelial  cells.  At 
all  events,  there  are  certainly  nuclei  in  the  basement  membrane. 
Beneath  the  basement  membrane  is  a  marginal  layer  of  a  more 
fibrillar  character.  This  is  closely  associated  with  the  mucosa,  and 
may  be  regarded  as  a  differentiation  of  the  latter.  Toward  the 
muscularis  mucosse  the  mucosa  is  terminated  by  a  reticulated  elastic 
membrane  (F.  P.  Mall,  in  the  dog),  containing  openings  for  the 
entrance  of  vessels,  nerves,  and  muscle-fibers. 

The  muscularis  mucoscz  consists  of  two  layers  of  unstriped 
muscular  fibers  arranged  in  a  manner  similar  to  that  in  the  external 
muscular  tunic — i.  e.y  having  an  inner  circular  and  an  outer  longi- 


THE    STOMACH    AND    INTESTINE. 


247 


tudinal  layer.  The  fibers  are  frequently  gathered  into  bundles, 
which  appear  to  be  separated  from  each  other  by  connective  tissue. 
From  both  layers,  but  more  especially  from  the  inner,  muscle-fibers 
are  given  off  at  right  angles,  which  enter  the  tunica  propria  and 
pass  between  the  glands  of  Lieberkuhn,  and  even  into  the  villi. 
In  the  latter  these  muscle-fibers  are  arranged  in  bundles,  and  lie 


Longitudinal 
muscular 
layer. 


Sphincter 
pylori. 


P---'Submucosa. 


Muscularis 
mucosae. 


Pyloric 
glands. 


'"•  Brunner's 
glands. 


""  Lymph- 
is  nodule. 


Villus. 


Longitudinal 
muscular 
layer. 


Circular  mus-T' 
cular  layer. 


Villus. 


Brunner's  glands. 


\Blood-vessel. 


'•••Glands  of  Lieberkuhn. 

Fig.  208. — Section  through  the  junction  of  the  human  pylorus  and  duodenum  ;  X  about 
15  :  At  a  the  pyloric  glands  extend  into  the  duodenum. 

near  their  axes  around  the  lacteal  vessels.     The  contraction  of  these 
fibers  causes  a  contraction  of  the  entire  villus. 

Lymph-nodules  are  distributed  throughout  the  mucosa  of  the 
small  intestine,  occurring  either  singly,  as  solitary  follicles,  or 
aggregated,  as  Peyer's  patches.  At  the  points  where  they  occur, 


248 


THE    DIGESTIVE    ORGANS. 


the  villi  are  absent  and  a  lateral  displacement  of  the  glands  of 
Lieberkuhn  is  observed.  The  lymph-nodule  is.  usually  pyriform  in 
shape.  The  thinner  portion  protrudes  somewhat  in  the  direction 
of  the  lumen  of  the  intestine,  while  the  thicker  portion  extends 
outward  to  the  muscularis  mucosae,  the  latter  being  frequently  in- 
dented or  even  perforated  if  the  lymph-nodules  be  markedly  devel- 
oped. Their  structure  is  similar  to  that  of  the  lymph-follicles  (see 
under  these),  and  consists  of  reticular  adenoid  tissue,  supporting 
lymph-cells.  It  should  be  remembered  that  every  nodule  may 
possess  a  germ  center.  Peyer's  patches  are  collections  of  these 
lymph-follicles.  The  surface  of  the  nodule  presenting  toward 
the  lumen  of  the  intestine  is  covered  with  a  continuous  layer  of 
intestinal  epithelium.  In  man  the  summit  of  that  portion  of  the 


Leucocyte 
in  epithe- 
lium. 
Epithelium.  -- 


Crypt,  .-y. 


Intermedi-  . 
ary  zone. 


Submucosa.  - 


Fig.   209. — Section  of  solitary  lymph-nodule  from  vermiform  appendix  of  guinea- 
pig,  showing  crypt ;  X  about  400  (Flemming's  fluid). 

nodule  projecting  into  the  lumen  of  the  intestine  presents  but  a 
slight  depression  of  the  intestinal  epithelium,  while  in  some  animals 
(guinea  -  pigs),  and  especially  in  the  nodules  composing  Peyer's 
patches,  there  is  a  deeper  depression,  even  leading  to  the  formation 
of  a  so-called  "crypt"  or  -"lacuna"  (uid.  Fig.  209).  At  the 
summit,  the  intestinal  epithelium  where  it  comes  in  contact  with 
the  lymph-nodule,  is  peculiarly  altered.  In  most  cases  there  is 
an  absence  of  a  basement  membrane,  the  epithelium  resting 
directly  upon  the  lymphoid  tissue.  No  clearly  defined  boundary 
between  the  two  is  distinguishable  (intermediate  zone  of  v.  David- 
off ) ;  they  are  therefore  in  the  closest  relationship  to  each  other. 
The  basal  surfaces  of  the  epithelial  cells  are  fibrillar,  the  fibrils 
seeming  to  penetrate  into  the  adenoid  reticulum  of  the  follicles. 


THE    STOMACH    AND    INTESTINE. 


249 


4.  THE  LARGE  INTESTINE,  RECTUM,  AND  ANUS. 

The  small  intestine  ends  at  the  ileocecal  valve.  At  some  dis- 
tance from  the  margin  of  the  valve  the  villi  of  the  ileum  become 
broad  and  low.  In  the  immediate  vicinity  of  the  valve  their  basilar 
portions  become  confluent,  forming  a  honeycomb  structure  which 
supports  a  few  villi.  At  the  base  of  the  honeycomb  open  the  glands 
of  Lieberkuhn.  On  the  cecal  side  of  the  valve  the  villi  become 
fewer  in  number  and  finally  disappear,  while  the  folds  which  give 
the  honeycomb  appearance  persist  for  a  considerable  distance.  In 


—5k  Intestinal  epithelium. 


—  Lumen  of  gland. 


—  Goblet  cell. 


Mucosa. 


—     Mucosa. 
- —     Muscularis  mucosae. 
Fig.  210. — From  colon  of  man,  showing  glands  of  Lieberkuhn  ;  X  2O°- 

the  adult  cecum  the  villi  are  absent.  The  mucosa  and  glands  pre- 
sent a  structure  similar  to  that  of  the  remainder  of  the  large  intes- 
tine. In  the  mucosa  of  the  vermiform  appendix  is  found  a  relatively 
large  number  of  solitary  lymph-follicles,  occasionally  forming  a 
continuous  layer.  The  marked  development  of  the  lymph-follicles 
encroaches  upon  the  glands  of  Lieberkuhn,  so  that  many  are 
obliterated  ;  they  are  penetrated  by  the  adenoid  tissue,  the  epithe- 
lial cells  of  the  glands  mingling  with  the  lymph-cells.  What  finally 


250 


THE    DIGESTIVE    ORGANS. 


becomes  of  the  secretory  cells  has  not  been  definitely  ascertained 
(Rudinger,  91). 

In  the  colon  the  villi  are  wanting,  while  the  glands  of  the 
mucosa  are  densely  placed  and  distributed  with  regularity. 

The  glands  of  Lieberkuhn  in  the  colon  are  somewhat  longer, 
and  as  a  rule  contain  many  more  goblet  cells  than  those  in  the  small 
intestine.  Only  the  neck  and  fundus  of  the  glands  show  cells  de- 
void of  mucus.  Transitional  stages  between  the  latter  and  the 
goblet  cells  have  been  observed  in  man  (Schaffer,  91).  Solitary 
lymph-follicles  are  found  throughout  the  colon.  They  are  situated 
in  the  mucosa,  only  the  larger  ones  extending  into  the  submucosa. 
The  glands  of  Lieberkuhn  are  displaced  in  the  regions  of  the  lymph- 
follicles. 


Gland. 


\ 


-    Submu- 
cosa. 


Fig.  211. — A  solitary  lymph- follicle  from  the  human  colon  :  At  a  is  seen  a  pronounced 
concentric  arrangement  of  the  lymph-cells. 

The  tcznice  and  pliccz  semilunares  cease  at  the  sigmoid  flexure, 
and  are  replaced  in  the  rectum  by  the  plicce  transversales  recti. 
Permanent  longitudinal  folds,  the  so-called  columns  rectales  Mor- 
gagni,  are  present  only  in  the  lower  portion  of  the  rectum.  Here  the 
intestinal  glands  are  longest  but  disappear  simultaneously  with 
the  rectal  columns.  At  the  anus  the  mucous  membrane  of  the 
rectum  forms  a  narrow  ring  devoid  of  glands,  covered  by  stratified 
pavement  epithelium,  and  terminating  in  the  skin  in  an  irregular 
line.  The  transition  from  the  mucous  membrane  to  the  skin  is 
gradual,  yet  reminding  one  of  the  appearance  presented  at  the 
junction  of  the  esophagus  with  the  cardiac  end  of  the  stomach. 

External  to  the  anus,  and  at  a  distance  of  about  one  centimeter 
from  it,  are  numerous  highly  developed  sweat-glands,  the  circum- 
anal  glands,  which  are  almost  as  large  as  the  axillary  glands. 


THE    STOMACH    AND    INTESTINE. 


251 


5.  BLOOD,  LYMPH,  AND  NERVE  SUPPLY  OF  THE  INTESTINE. 

In  general,  the  following  holds  true  with  regard  to  the  blood- 
vessels of  the  intestinal  tract  (further  details  will  be  discussed  in 
dealing  with  the  vessels  of  the  various  regions  of  the  intestine)  : 
The  arteries  enter  along  the  line  of  the  mesenteric  attachment  and 
penetrate  the  longitudinal  muscular  layer.  Between  the  two  mus- 
cular layers  branches  are  given  off  which 'form  an  intermuscular 
plexus,  from  which,  in  turn,  smaller  branches  pass  out  to  supply 
the  muscles  themselves.  The  arterial  trunks  penetrate  the  circu- 
lar muscular  layer  and  form  an  extensive  network  of  larger 
vessels  in  the  deeper  layer  of  the  submucosa.  This  is  known 
as  Heller's  plexus  (F.  P.  Mall).  From  this,  radiating  branches  are 


—  Epithelium  of 
stomach. 


—  Region  of  the 
bodies  of  the 
gastric  glands. 


-  -•  Muscularis  mucosae. 


Fig.  212. — Section  through  fundus  of  cat's  stomach.     The  blood-vessels  are 
injected ;  X  oo- 


given  off  which  supply  the  muscularis,  mucosae,  forming  under 
the  latter  a  close  network  of  finer  vessels.  This  plexus,  together 
with  that  of  Heller,  gives  rise  to  vessels  which  penetrate  the  mus- 
cularis mucosae  and  break  up  into  capillaries  in  the  mucous  mem- 
brane. The  veins  of  the  mucous  membrane  form  beneath  the 
muscularis  mucosae  a  plexus  with  small  meshes,  giving  off  many 
radiating  branches  ;  these  in  turn  unite  to  form  an  extensive  net- 
work of  coarser  vessels.  Veins  extend  from  the  latter  and  unite 
to  form  larger  trunks,  which  then  lie  side  by  side  with  the  arteries. 
According  to  F.  P.  Mall,  delicate  retia  mirabilia  occur  here  and 
there  in  the  venous  network  in  the  submucosa  of  the  intestine  of 
the  dog. 

In  the  esophagus  the  arteries  end  in  a  capillary  network  situated 


252  THE    DIGESTIVE    ORGANS. 

in  the  mucosa  and  extending  into  the  connective-tissue  papillae  of 
the  mucosa. 

The  vessels  of  the  stomach  are  arranged  in  plexuses  in  the 
muscular  coat,  submucosa,  and  beneath  the  muscularis  mucosae,  as 
previously  described.  From  the  plexus  beneath  the  muscularis  mu- 
cosae,  small  branches  are  given  off  which  pass  through  this  layer  and 
in  the  mucosa  form  a  capillary  network,  consisting  of  relatively  small 
capillaries,  which  surround  the  gastric  glands,  this  plexus  being  par- 
ticularly well  developed  in  the  region  around  the  body  and  neck  of 
the  glands,  where  the  parietal  cells  are  most  numerous.  The  capil- 
laries of  this  network  are  continuous  with  capillaries  of  a  much  larger 
size,  forming  a  network  surrounding  the  gastric  crypts  and  situated 
immediately  under  the  epithelium  lining  the  mucosa  of  the  stomach. 
The  blood  is  collected  from  this  capillary  plexus  by  small  veins 
which  pass  nearly  perpendicularly  through  the  mucosa,  forming  a 
plexus  above  the  muscularis  mucosae,  from  which  small  veins  pass 
through  the  muscularis  mucosae  to  the  venous  plexus  in  the  sub- 
mucosa. 

The  blood-vessels  of  the  mucosa  of  the  small  intestine  may  be 
divided  into  (i)  the  arteries  of  the  villi  and  (2)  the  arteries  of  the 
intestinal  glands.  The  former  arise  principally  from  the  deep  arterial 
network  in  the  submucosa,  then  penetrate  the  muscularis  mucosae 
and  give  off  branches  at  acute  angles  which  continue  without 
further  branching  into  the  summits  of  the  villi.  Within  the  villi 
themselves  the  arteries  lie  in  the  axes.  The  broader  villi  may 
contain  two  arteries.  The  circular  muscle-fibers  of  the  arteries 
gradually  disappear  inside  of  the  villi  (dog),  and  at  the  summit  of 
the  latter  the  vessels  break  up  into  a  large  number  of  capillaries. 
These  form  a  dense  network  extending  beneath  the  basement  mem- 
brane and  into  its  marginal  layer.  These  networks  give  rise  to 
venous  capillaries  which  unite  to  form  small  vessels  and  finally  end 
in  two  or  more  larger  veins  inside  of  the  villi.  These  latter  are  con- 
nected with  the  venous  network  in  the  mucosa. 

The  glandular  arteries,  derived  principally  from  the  superficial 
network  of  the  submucosa,  also  pass  through  the  muscularis 
mucosae  and  break  up  internally  into  capillary  nets  which  encircle 
the  intestinal  glands  ;  these  give  rise  to  small  veins  which  empty 
into  the  venous  plexus  of  the  mucosa.  The  veins  of  the  plexus  in 
the  mucosa  unite  to  form  larger  branches,  which  connect  with  the 
plexus  in  the  submucosa  (compare  Fig.  213).  In  the  dog  these 
trunks  inside  of  the  muscularis  mucosae  are  encircled  by  bundles  of 
muscle-fibers  (sphincters,  F.  P.  Mall).  The  capillaries  of  the  solitary 
lymph-nodules  do  not  always  penetrate  into  the  centers  of  the  latter, 
but  often  leave  a  central  nonvascular  area. 

The  blood-vessels  of  the  mucosa  of  the  large  intestine  are,  in 
their  distribution,  similar  to  the  glandular  vessels  of  the  small  intes- 
tine and  stomach. 

The  lymph-vessels  begin  in  the  mucosa  near  the  epithelium,  pass 


THE    STOMACH    AND    INTESTINE. 


253 


down  between  the  glands,  and  are  arranged  in  the  form  of  a  net- 
work just  above  the  muscularis  mucosae,  but  with  coarser  meshes 
than  that  formed  by  the  blood-vessels.  Here  the  valves  begin  to 
make  their  appearance.  The  lymph-vessels  pass  through  the  mus- 
cularis mucosae  and  in  the  outer  portion  of  the  submucosa  form  a 
plexus  with  open  meshes,  from  which  are  derived  the  efferent  ves- 
sels which  penetrate  the  muscular  coat  and  thus  gain  access  to  the 
mesentery.  In  their  course  through  the  muscular  coat  they  com- 
municate with  the  branches  of  a  plexus  of  lymph-vessels  situated 
between  the  two  muscular  layers,  and  also  with  lymph-vessels  found 
in  the  serous  coat. 


Epithelium 
of  villus. 


a~-/-r-    Chyle-vessel. 


Central  chyle- 
vessel  of  vil- 
lus. 


Artery.     ---r^;__^ 


-  Mucosa. 

"  Muscularis 
mucosae. 

-  Submucosa. 

Plexus  of 
lymph  -  ves- 
sels. 

Circular  mus- 
cular layer. 

Plexus  of 
lymph-ves- 
sels. 

Long.  muse, 
layerwiththe 
serous  coat. 


Fig.  213. Schematic  transverse  section  of  the  human  small  intestine  (after  F.  P.  Mall). 

The  lymphatics  of  the  small  intestine  begin  in  the  axes  of  the 
villi.  When  filled,  these  lymph-vessels  are  conspicuous,  irregularly 
cylindric  capillary  tubules,  'lined  by  endothelial  cells,  and  known  as 
the  axial  canals,  the  chyle-vessels,  or  \hzlacteals  of  the  villi.  They 
are  hardly  discernible  when  collapsed.  If  the  villus  be  broad,  it 
may  contain  two  chyle-vessels,  which  then  join  at  the  apex  of  the 
villus,  and  may  also  be  connected  with  each  other  by  a  few  anasto- 
moses. At  the  base  of  the  villus  the  chyle-vessel  enters  a  lymphatic 
capillary  network,  the  structure  of  which  is  due  to  the  confluence 


254  THE    DIGESTIVE    ORGANS. 

of  similar  canals.  Numerous  lymph-vessels  from  this  network 
penetrate  the  mucous  membrane  in  a  vertical  direction,  uniting  at 
the  bases  of  the  intestinal  glands  to  form  a  second  plexus — sub- 
glandular  plexus  of  the  mucosa.  A  few  of  the  lymph-vessels  pene- 
trating the  mucous  membrane  directly  perforate  the  muscularis 
mucosae  to  join  the  lymphatic  network  of  the  submucosa.  The 
subglandular  plexus  also  communicates  with  the  submucous 
lymphatic  plexus  by  means  of  small  radiating  branches  (vid.  Fig. 
213).  The  solitary  lymph-nodules  themselves  contain  no  lymphatic 
vessels,  but  are  encircled  at  their  periphery  by  a  network  of  lymph 
capillaries.  The  same  is  true  of  the  nodules  in  Peyer's  patches. 
It  is  an  interesting  fact  that  in  the  rabbit  lymph-sinuses  exist 
around  Peyer's  patches,  giving  to  the  latter  a  still  greater  similarity 
to  the  nodules  of  lymph-glands.  The  solitary  nodules  of  the  same 


Fig.  214. — A  portion  of  the  plexus  of  Auerbach  from  stomach  of  cat,  stained  with 
methylene-blue  (infra  vitani],  as  seen  under  low  magnification. 

animal  are   not  surrounded  by  the  sinuses  just  mentioned  (Stohr, 

94)- 

The  structures  of  the  alimentary  canal  receive  their  innervation 
mainly  from  sympathetic  neurones,  the  cell-bodies  of  which  are 
grouped  to  form  small  ganglia,  located  at  the  nodal  points  of  two 
plexuses,  one  of  which  is  situated  between  the  two  layers  of  the 
muscular  coat,  the  other  in  the  submucosa.  These  two  plexuses 
are  found  in  the  entire  digestive  tract,  although  not  equally  well 
developed  in  its  different  regions.  The  outer  plexus,  the  more 
prominent  of  the  two,  situated  between  the  two  layers  of  the  muscu- 
lar coat,  is  known  as  the  plexus  myentericiis,  or  the  plexus  of  Auer- 
bach. It  consists  of  innumerable  small  sympathetic  ganglia,  united 
by  small  bundles  of  nonmedullated  fibers,  containing  here  and  there 
a  much  smaller  number  of  medullated  nerve-fibers.  The  cell-bodies 
of  the  sympathetic  neurones  of  this  plexus  are  grouped  to  form  the 


THE    STOMACH    AND    INTESTINE. 


255 


sympathetic  ganglia.  The  dendrites,  the  number  of  which  varies 
for  the  different  cells,  divide  and  redivide  in  the  ganglia,  some  ex- 
tending into  the  nerve  bundles  uniting  the  ganglia.  The  neuraxes 
of  the  sympathetic  neurones  of  the  ganglia  form  nonmedullated 
nerve-fibers,  which  leave  the  ganglia  by  one  of  the  several  roots 
possessed  by  each  ganglion,  and,  after  repeated  division  and  forming 
intricate  plexuses  in  the  circular  and  longitudinal  layers  of  the  mus- 
cular coat,  terminate  on  the  involuntary  muscle-cells  of  these  layers. 

The  plexus  in  the  submucosa,  known  as  the  plexus  of  Meissner, 
is  similarly  constructed,  although  it  contains  fewer  and  much  smaller 
ganglia  and  the  meshes  of  the  plexus  are  much  finer.  It  commu- 
nicates by  numerous  anastomoses  with  the  plexus  of  Auerbach. 
The  neuraxes  of  the  sympathetic  neurones  of  this  plexus  have  not 
been  traced,  with  any  degree  of  certainty,  to  their  terminations. 
Numerous  nonmedullated  nerves  enter  the  muscularis  mucosae  and, 
according  to  Berkley  (93,  I),  form  in  the  dog  terminal  bulbs  and 
nodules  which  perhaps  rep- 
resent the  endings  of  motor 
(sympathetic)  nerves  in  this 
layer.  Nerve-fibers  have  also 
been  traced  into  the  mucosa, 
and  in  the  vicinity  of  the 
glands  and  in  the  villi  are 
found  numerous  exceedingly 
fine  nerve-fibers  which  inter- 
lace, but  in  the  greater  por- 
tion of  the  intestinal  tract  the 
endings  of  these  fibers  have 
not  been  fully  worked  out. 
That  they  end  on  the  gland- 
cells  seems  very  probable 
from  observations  made  by 
Kytmanow  (96),  who  was 

able,  by  means  of  the  methylene-blue  method,  to  stain  plexuses 
of  fine  nerve-fibrils  surrounding  the  gastric  glands  of  the  cat,  some 
of  these  fibrils  being  traced  through  the  basement  membrane  of 
the  glands  and  to  and  between  the  gland-cells,  where  they  ter- 
minated in  clusters  of  small  nodules  on  both  the  chief  and  parietal 
cells.  The  plexus  of  Meissner  is  not  so  well  developed  in  the 
esophagus  as  in  the  remaining  portions  of  the  digestive  tract. 

That  the  cell-bodies  of  many  of  the  sympathetic  neurones  of 
Auerbach's  and  Meissner's  plexuses  are  capable  of  being  stimulated 
by  cerebrospinal  nerves  seems  certain  from  observations  made  by 
Dogiel  (95),  who  has  shown  that  many  small  medullated  nerve- 
fibers  which  enter  the  digestive  tract  through  the  mesentery  (small 
and  large  intestines)  terminate  after  repeated  division  in  terminal 
end-baskets  which  surround  the  cell-bodies  of  many  of  the  sympa- 
thetic neurones  of  these  plexuses.  Similar  nerve-fibers  ending  in 


Fig.  215.  — From  thin  section  of  esophagus 
of  cat,  showing  the  epithelium  and  a  portion 
of  the  mucosa  and  the  terminal  nerve-fibrils  in 
the  epithelium  (from  preparation  of  Dr.  DeWitt). 


256  THE    DIGESTIVE    ORGANS. 

baskets  have  also  been  observed  in  the  ganglia  of  the  plexuses  of 
the  stomach  and  esophagus.  Large  medullated  nerve-fibers,  the 
dendrites  of  sensory  neurones,  have  also  been  traced  to  the  alimen- 
tary canal.  In  the  esophagus  these  pass  to  the  mucosa,  where, 
after  repeated  division,  they  lose  their  medullary  sheaths,  the  non- 
medullated  terminal  branches  forming  a  subepithelial  plexus  from 
which  terminal,  varicose  branches,  further  dividing,  enter  the  strati- 
fied epithelium  and  may  be  traced  to  near  the  surface  of  the  epithe- 
lium. 

Large  medullated  nerve-fibers  may  be  traced  through  the 
ganglia  of  Auerbach's  and  Meissner's  plexuses  in  the  stomach  and 
intestinal  canal  and  through  the  nerve  bundles  uniting  these  ganglia 
(Dogiel,  99),  but  the  termination  of  these  fibers  has  not  been  deter- 
mined. 


6.  THE  SECRETION  OF  THE  INTESTINE  AND  THE  ABSORPTION 

OF  FAT. 

The  cells  of  Brunner's  glands  are  similar  in  many  respects  to 
those  of  the  pyloric  glands.  During  digestion  they  show  analogous 
changes — i.  e.,  the  secretory  cells  are  large  and  clear  during  a  state 
of  hunger,  and  become  smaller  and  opaque  during  the  process  of 
secretion.  Another  and  still  greater  similarity  between  Brunner's 
glands  and  the  pyloric  glands  is  established  by  the  fact  that  the  cells 
of  the  former,  especially  during  hunger,  have  been  shown  to  be  rich 
in  pepsin.  It  is  well  known  that  the  goblet  cells  of  the  intestinal 
glands  are  very  numerous  during  starvation,  and  that  they  nearly 
disappear  after  continued  functional  activity  ;  furthermore,  they  en- 
tirely disappear  in  certain  portions  of  the  rabbit's  intestine  after 
pilocarpin-poisoning.  It  would  therefore  appear  that  the  principal 
physiologic  function  of  the  glands  of  Lieberkiihn  is  to  secrete  mucus, 
although  the  possibility  of  the  production  of  another  secretion, 
especially  in  the  small  intestine,  must  not  be  excluded  (compare  R. 
Heidenhain,  83). 

Until  recently  it  was  believed  that  the  fat  contained  in  the  food 
was  emulsified  in  the  intestine,  and  furthermore  that  the  bile  acted 
upon  the  cuticular  margins  of  the  epithelial  cells  in  the  villi  in  such  a 
manner  that  an  assimilation  of  the  emulsified  fat  by  the  cells  of  the 
villi  (not  by  the  goblet  cells)  was  made  possible.  It  has  been  re- 
peatedly observed  that  the  epithelial  cells  contained  fat  granules 
during  absorption.  Hence  a  mechanism  was  sought  for  which 
would  account  for  an  assimilation  of  globules  of  emulsified  fat  on 
the  part  of  the  cells.  It  seemed  most  probable  that  protoplasmic 
threads  (pseudopodia)  were  thrown  out  from  each  cell  through  its 
cuticular  zone,  which,  after  taking  up  the  fat,  withdrew  with  it  again 
into  the  cell.  But  when  it  was  shown  that,  after  feeding  with  fatty 
acids  or  soaps,  globules  of  fat  still  appeared  in  the  epithelial  cells  as 
before,  and  that  the  chyle  also  contained  fat,  the  hypothesis  was 


THE    LIVER.  257 

suggested  that  the  fat  is  split  up  by  the  pancreatic  juice  into  glycerin 
and  fatty  acids,  and  that  the  fatty  acids  are  then  dissolved  by  the 
bile  and  the  alkalies  of  the  intestinal  juice,  only  again  to  combine 
with  the  glycerin  to  form  fat  within  the  epithelial  cells.  It  remains 
for  the  histologist  to  ascertain  the  exact  mechanism  in  the  cell  which 
changes  the  fatty  acids  into  fat.  Altmann  (94)  claims  that  certain 
granules  of  the  cells  (elementary  organisms)  offer  a  solution  to  this 
problem.  The  manner  in  which  the  fat  globules  gain  access  to  the 
central  vessels  of  the  villi  is  a  question  which  has  not  as  yet  been 
settled. 

D*  THE  LIVER. 

In  the  adult  the  liver  is  a  lobular,  tubular  gland  with  anastomos- 
ing tubules.  When  viewed  with  the  unaided  eye  or  under  low 
magnification  the  liver  is  seen  to  be  composed  of  a  large  number 


Intralobular 
vein. 


Branch  of 

hepatic 

artery. 
Interlobular 

connective 

tissue. 


Fig.  2 1 6. — Section  through  liver  of  pig,  showing  chains  of  liver-cells  ;    X  7°- 

of  nearly  spheric  divisions  of  equal  size  ;  this  is  particularly  notice- 
able in  some  animals,  especially  in  the  pig.  These  divisions  are  the 
liver  lobules  and  have  a  diameter  of  from  0.7  to  2.2  mm.  They  are 
separated  from  each  other  by  a  varying  amount  of  interlobular  con- 
nective tissue,  which  is  a  continuation  of  the  capsule  of  Glisson,  a 
fibre-elastic  layer  surrounding  the  entire  liver  and  covered  for  the 
greater  portion  by  a  layer  of  mesothelium.  In  the  interlobular 
septa  are  found  the  larger  blood-vessels,  bile  passages,  nerves  and 
lymph-vessels.  On  examining  a  thick  section  of  the  liver  with  a 
low  power,  a  radiate  structure  of  the  lobule  is  noticeable,  and  an 
open  space  is  seen  in  its  center,  which  according  to  the  direction  of 
the  section,  is  either  completely  surrounded  by  liver  tissue  or  con- 
nected with  the  periphery  of  the  lobule  by  a  canal.  This  open 
'7 


258 


THE    DIGESTIVE    ORGANS. 


space  represents  the  central  or  intralobular  vein  of  the  lobule  which 
belongs  to  the  system  of  the  inferior  vena  cava.  From  the  center 
of  the  lobule  toward  its  periphery  extend  numerous  radiating 
strands  of  cells,  which  branch  freely  and  anastomose  with  each 
other,  and  are  known  as  the  trabeculcz,  or  cords  of  hepatic  cells.  Be- 
tween the  latter  are  small,  clear  spaces  occupied  partly  by  blood 
capillaries  and  partly  by  the  intralobular  connective  tissue.  The  above 
description  is  in  some  respects  not  a  true  statement  of  the  appear- 
ance presented  by  the  human  liver,  as  in  the  latter  one  or  more 
lobules  may  blend  with  each  other,  thus  rendering  the  individual 
lobules  less  distinct. 

The  hepatic  cords  consist  of  rows  of  hepatic  cells.     The  cells 


Portal   inter- 
lobular 
branch, cut 
longitudi- 
nally. 


The  same,  cut 
transversely. 


Fig.  217. — Section  through  injected  liver  of  rabbit.     The  boundaries  of  the  lobules 
are  indistinct ;  X  about  35. 

are  usually  polyhedral  in  form,  with  surfaces  so  approximated  that 
a  cylindric  capillary  space,  known  as  the  bile  capillary  remains  be- 
tween them.  The  angles  of  the  cells  also  show  grooves  which 
join  those  of  the  neighboring  cells  to  form  canals  in  which  lie  the 
blood  capillaries.  A  closer  examination  of  the  hepatic  cells  reveals 
the  fact  that  they  possess  no  distinct  membrane,  and,  in  a  resting 
state,  usually  contain  a  single  nucleus,  although  some  possess  two. 
It  is  an  interesting  fact  that  nearly  all  the  hepatic  cells  of  some 
animals — as,  for  instance,  the  rabbit — contain  two  nuclei.  The 
cell-bodies  of  the  hepatic  cells,  which  average  from  i8//  to  26 //  in 
diameter,  show  a  differentiation  into  protoplasm  and  paraplasm. 
This  is  especially  manifest  in  a  state  of  hunger.  In  this  condition 


THE    LIVER. 


259 


it  is  seen  that  the  network  of  protoplasm  around  the  nucleus  is  un- 
usually dense,  and  becomes  looser  in  arrangement  as  it  extends 
toward  the  periphery  of  the  cell-body.  The  paraplasm  is  slightly 
granular,  and  contains  glycogen  and  bile  drops  during  the  func- 
tional activity  of  the  cell  (secretion  vacuoles).  The  vacuoles  in  the 
paraplasm  play  an  important  part  in  the  secretion  of  the  cell,  and  are 


Intralobular 
vein. 


Fig.  218. — Human  bile  capillaries.  The  capillaries  of  one  lobule  are  seen  to  anas- 
tomose with  those  of  the  adjoining  lobule  (below,  in  the  figure)  ;  X  IIQ  (chrome-silver 
method). 


Vacuole  of  secretion.     ----- 


Tubule  of  same. 
Bile  capillary. 


Fig.  219. — Human  bile  capillaries  as  seen  in  section  ;   X  4^o  (chrome-silver  method). 


due  to  the  confluence  of  minute  drops  of  bile  into  a  large  globule. 
As  soon  as  the  vacuole  has  attained  a  certain  size  it  tends  to  empty 
its  contents  into  the  bile  capillary  through  a  small  tubule  connect- 
ing the  vacuole  with  the  bile  capillary  (Kupffer,  73,  89). 

The  bile  capillaries  are,  as  we  have  remarked,  nothing  but  tubu- 
lar, capillary  spaces  between  the  hepatic  cells,  with  no  distinct  indi- 


260 


THE    DIGESTIVE    ORGANS. 


vidual  walls.  They  may  be  compared  to  the  lumen  of  a  tubular 
gland,  although  in  the  human  liver  their  walls  consist  of  only  two 
rows  of  'hepatic  cells.  In  the  lower  vertebrates  the  walls  of  the 
bile  capillaries  appear  in  transverse  section  to  consist  of  several 
cells  (in  the  frog  generally  three,  in  the  viper  as  many  as  five).  The 
bile  capillaries  naturally  follow  the  course  of  the  hepatic  cords — /.  e., 
in  man  extending  radially.  They  form  networks,  the  meshes  of 
which  correspond  to  the  size  of  the  hepatic  cells.  At  the  periphery 
of  the  lobule  the  hepatic  cells  pass  directly  over  into  the  epithelial 
cells  of  the  smaller  interlobular  bile-ducts.  The  epithelium  of  the 
latter  is  of  the  cubical  variety,  its  cells  being  considerably  smaller  than 
the  hepatic  cells.  At  the  point 

where  the  hepatic  cells  become  ^^^  _n  Bile  capillaries. 
continuous  with  the  walls  of  the 
smaller  passages  we  find  a  few 
cells  of  gradually  decreasing  size 
which  represent  a  transition  stage 
from  the  cells  of  the  bile  capil- 


Fig.  220. — Schematic  diagram  of  he- 
patic cord  in  transverse  section.  At  the 
left  the  bile  capillary  is  formed  by  four  cells, 
at  the  right  by  two ;  the  latter  type  occurs 
in  the  human  adult. 


Fig.  221. — From  the  human  liver, 
showing  the  beginning  of  the  bile -ducts  ; 
X  90  (chrome-silver). 


laries  (hepatic  cells)  to  those  of  the  interlobular  bile  passages. 

The  vascular  system  of  the  liver  is  peculiar  in  that,  besides 
the  usual  arterial  and  venous  vessels  common  to  all  organs, 
there  is  found  another  large  afferent  vein — the  portal  vein.  It 
arises  from  a  confluence  of  the  superior  and  inferior  mesenteric, 
the  splenic,  coronary  veins  from  the  stomach,  and  cystic  veins. 
It  divides  into  two  branches,  the  right  supplying  the  right  lobe 
of  the  liver,  the  left  the  remaining  lobes.  These  branches  again 
divide  into  numerous  smaller  branches,  the  smallest  of  which 
finally  reach  the  individual  lobules.  While  still  within  the  inter- 
lobular tissue,  the  branches  of  the  portal  vein  receive  the  venous 
blood  from  the  hepatic  arterial  system.  These  smaller  divisions 
constitute  the  internal  radicals  of  the  portal  vein,  since  they  are 
within  the  liver  itself.  Along  its  whole  course  through  the  inter- 
lobular connective  tissue  the  portal  vein  and  its  branches  are  accom- 
panied by  divisions  of  the  hepatic  artery  and  bile  passages.  In  a 
transverse  section  of  the  liver  the  arrangement  of  these  structures 
in  the  interlobular  tissue  is  such  that  the  cross-sections  of  the  vessels 


THE    LIVER.  26l 

belonging  to  the  hepatic  vein  are  seen  to  be  at  some  distance  from 
the  closely  approximated  branches  of  the  portal  vein  and  bile  pas- 
sages. Branches  of  the  portal  vein  encircle  the  liver  lobules  at 
different  points,  and  while  they  remain  within  the  interlobular  con- 
nective tissue,  are  known  as  interlobular  veins.  From  these,  small 
offshoots  are  given  off  to  the  lobules  which,  on  entering,  divide  into 
capillaries  and  form  a  closely  reticulated  network  between  the 
hepatic  cords.  The  meshes  of  this  network  are  about  as  large 
as  an  hepatic  cell,  each  cell  coming  in  repeated  contact  with  the 
blood  capillaries.  All  of  these  capillaries  pass  toward  the  central 
or  intralobular  vein  of  the  lobule,  which  during  its  efferent  passage 
through  the  lobule  continues  to  receive  capillaries  from  the  portal 


Blood  capillaries. 


Intralobular  vein. 


-  Cord  of  hepatic 

cells. 


Interlobular  vessel. 


Fig.  222. — Injected  blood-vessels  in  liver  lobule  of  rabbit ;  X  Io°- 

system.  The  intralobular  veins  unite  to  form  the  sublobular  veins, 
situated  in  the  interlobular  connective  tissue,  and  these  unite  to  form 
the  larger  hepatic  veins  which  empty  into  the  inferior  vena  cava. 
The  relations  of  the  various  blood-vessels  within  the  lobule  are  in 
themselves  somewhat  difficult  of  comprehension,  but  the  whole  be- 
comes still  more  complicated  when  the  reciprocal  relations  of  the 
vessels  and  bile  capillaries  are  taken  into  consideration.  In  order 
to  understand  the  structure  of  the  liver  lobule,  with  its  hepatic 
cords,  vessels,  and  bile  capillaries,  the  following  points  should  be 
borne  in  mind  :  The  course  of  the  bile  capillaries  is  along  the  sur- 
faces, and  that  of  the  blood-vessels  along  the  angles  of  the  hepatic 
cells  ;  every  cell  comes  in  contact  with  a  bile  capillary  and  a  blood 


262  THE    DIGESTIVE    ORGANS. 

capillary.  The  latter,  however,  do  not  come  in  contact  with  the 
former,  but  in  man  are  separated  by  at  least  half  the  breadth  of  a 
hepatic  cell.  In  animals  in  which  the  bile  capillaries  are  bounded 
by  more  than  two  cells,  the  blood-vessels  extend  along  the  outer 
sides  of  the  hepatic  cells  ;  here  the  bile  and  blood  capillaries  are 
separated  from  each  other  by  the  breadth  of  a  whole  cell. 

The  connective  tissue  within  the  hepatic  lobules  presents  points 
of  interest  which,  however,  are  not  demonstrable  in  organs  treated 
by  ordinary  methods.  But  when  the  liver  tissue  is  treated  by  a 
certain  special  method  (vid.  T.  258),  an  astounding  number  of  fibers 
are  seen  extending  in  regular  arrangement  from  the  periphery  toward 
the  central  vein.  These  fibers  are  extremely  delicate,  of  nearly 
equal  size,  and  intermingle  in  such  a  manner  as  to  form  an  envel- 
oping network  about  the  blood  capillaries  (Gitterfasern  ;  Kupffer ; 


Boundary  of  - 
lobule. 


-  Intralobular 
vein. 


Fig.  223.— Reticulum  (Gitterfasern)  of  dog's  liver;  X  I2°  (gold-chlorid  method). 


Oppel,  91  ;  vid.  Fig.  223).  A  few  coarser  fibers  (radiate  fibers, 
Kupffer,  73)  seem  to  enter  in  a  less  degree  into  the  formation  of  the 
sheath  around  the  blood  capillaries  ;  they  also  extend  from  the 
periphery  toward  the  center  of  the  lobule  and  form  a  coarse  reticu- 
lum,  the  meshes  of  which  are  drawn  out  radially.  The  radiate 
fibers  are  less  prominent  in  man,  but  are  numerous  and  well  devel- 
oped in  animals  (rat,  dog).  With  what  exuberance  the  intralobular 
connective  tissue  may  develop,  is  seen  in  the  accompanying  sketch 
of  a  sturgeon's  liver,  which  is  taken  from  one  of  Kupffer's  prepara- 
tions. 

Certain  peculiar  cells — the  so-called  stellate  cells  of  Kupffer  (76) 
— occur  exclusively  in  the  lobule,  and  are  seen  only  after  a  special 
method  of  treatment.  They  are  uniformly  distributed,  of  differ- 
ent shapes,  elongated,  and  end  in  two  or  three  pointed  projec- 


THE    LIVER.  263 

tions.  They  are  smaller  than  the  hepatic  cells,  and  contain  one  or 
two  nuclei. 

In  a  recent  communication  Kupffer  (99)  states  that  the  stellate 
cells  belong  to  the  endothelium  of  the  intralobular  capillaries  of  the 
portal  vein.  In  such  cells  blood-corpuscles  and  fragments  of  such 
were  often  found.  The  endothelium  of  these  capillaries  possesses, 
therefore,  a  phagocytic  function,  taking  up  particles  of  foreign  mat- 
ter, blood-corpuscles,  etc. 

The  efferent  ducts  of  the  liver,  the  bile-ducts,  are  lined  by  col- 
umnar epithelium,  varying  in  height  in  direct  proportion  to  the  cal- 
iber of  the  passage.  The  smallest  ducts  possess  a  low,  the  medium 
sized  a  cubical,  and  the  larger  a  columnar  epithelium.  The  smaller 
bile-ducts  have  no  clearly  defined  external  walls  other  than  the 
membrana  propria  ;  the  larger  ones,  on  the  other  hand,  possess  a 


Connective-tissue 
fibers. 


Fig.  224. — Connective  tissue  from  liver  of  sturgeon.    At  a  is  an  open  space  from  which 
the  hepatic  cells  were  mechanically  removed  during  treatment. 

connective-tissue  sheath  which  may  even  present  two  layers  in  the 
larger  passages.  Unstriped  muscular  fibers  occur  in  the  large 
ducts,  but  do  not  form  a  continuous  layer  until  the  gall-bladder 
is  reached,  where  two  layers  are  found.  The  epithelium  of  the 
gall-bladder  is  of  the  columnar  variety,  with  nuclei  in  the  lower 
thirds  of  the  cells  ;  a  cuticular  zone  is  either  absent  or  very  poorly 
developed.  The  mucous  membrane  of  the  gall-bladder  is  raised 
into  folds  having  a  peculiar  reticular  arrangement  The  gall-bladder 
contains  a  few  mucous  glands  ;  these  are,  however,  more  numerous 
in  the  hepatic,  cystic,  and  common  bile-ducts. 

Besides  the  network  of  lymph-vessels  accompanying  the  portal 
vein  and  hepatic  artery,  there  are  also  lymphatic  networks  about 
the  branches  of  the  hepatic  vein  (v.  Wittich).  The  lymph-ves- 
sels penetrate  the  liver  lobules  and  pass  between  the  hepatic  cells 


264  THE    DIGESTIVE    ORGANS. 

and   the   blood   capillaries   to   form   perivascular  capillary  lymph- 
spaces. 

Berkley  (94)  has  described  several  divisions  of  the  intrinsic  nerves 
of  the  liver,  all  connected  and  morphologically  alike.  These  nerves 
are  no  doubt  the  neuraxes  of  sympathetic  neurones,  the  cell-bodies 
of  which  are  located  in  ganglia  outside  of  this  organ.  No  medul- 
lated  fibers  were  found  by  him,  although  it  seems  probable  that  the 
nerve-fibrils  terminating  between  the  cells  of  the  bile-ducts  (see  be- 
low) are  terminal  branches  of  sensory  nerve-fibers.  The  nerves  of 
the  liver  accompany  the  portal  vessels,  the  hepatic  arteries,  and  the 
bile-ducts.  The  first  division  of  the  nerves,  embracing  the  larger 
number  of  the  intrinsic  hepatic  nerves,  accompany  the  branches 
of  the  portal  vessels,  form  plexuses  about  them,  and  end  in  inter- 
lobular  and  intralobular  ramifications,  the  latter  showing  here  and 
there  knob-like  terminations  on  the  liver-cells,  and,  in  their  course, 
give  off  here  and  there  branches  which  end  on  the  portal  vessels. 


— Interlobular  con- 
nective tissue. 


^".%    ..:.tv^^ 

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^ 

t  •;  ^;.   :\,:>  -:^i%.__.._ 

^£s  !>•>•* 
^f*'.^  -•#?'.-''  •  ^ 

•  vV/-''.Y."V"  -^ 

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S^S«?S  I 

*      "'       *     ^<      '*     '"-* Stellate  cells. 


Fig.  225. — Part  of  a  section  through  liver  lobule  from  dog,  showing  stellate  cells  ; 
X  1 68  (vid.  T.  257). 

The  nerve-fibers  following  the  hepatic  arteries  are  in  every  respect  like 
the  vascular  nerves  in  other  glands.  Some  of  the  terminal  branches 
seem,  however,  to  end  on  hepatic  cells.  The  nerve-fibers  following 
the  bile-ducts  may  be  traced  to  the  smaller  and  medium-sized 
ducts,  forming  a  network  about  them,  and  ending  here  and  there 
in  small  twigs  on  the  outer  surface  of  the  cells,  and  occasionally, 
it  would  seem,  between  the  epithelial  cells  lining  the  ducts.  The 
suggestion  seems  warranted  that  these  terminal  fibrils  are  the  end- 
ings of  sensory  nerves.  Some  of  the  nerve-fibers  following  the 
bile-ducts  may  be  traced  into  the  hepatic  lobules.  The  intralobu- 
lar plexus  is  formed,  therefore,  by  the  terminal  branches  of  the  non- 
medullated  nerve-fibers  accompanying  the  portal  and  hepatic  ves- 
sels and  the  bile-ducts.  In  the  wall  of  the  gall-bladder  are  found 
numerous  small  sympathetic  ganglia  formed  by  the  grouping  of  the 
cell-bodies  of  sympathetic  neurones  (Dogiel).  The  neuraxes  of  these 


THE    PANCREAS. 


265 


innervate  the  nonstriated  muscle  of  this  structure.  Large,  medul- 
lated  nerve-fibers  may  be  traced  through  these  ganglia  which 
appear  to  end  in  free  sensory  endings  in  and  under  the  epithelium 
lining  the  gall-bladder  (Huber). 

In  the  human  embryo  the  liver  originates  from  the  intestine 
during  the  second  month  as  a  double  ventral  diverticulum.  Later 
solid  trabecular  masses  are  developed  which  then  unite  and  become 
hollow.  At  this  stage  the  whole  gland  is  uniform  in  structure,  as 
a  division  into  lobules  does  not  take  place  until  later.  The  bile 
capillaries  are  surrounded  by  more  than  two  rows  of  cells.  In  this 
stage  the  embryonal  liver  suggests  a  condition  which  is  permanent 
during  the  life  of  certain  animals.  Only  later  when  the  venae  ad- 
vehentes,  which  later  represent  the  branches  of  the  portal  vein, 
penetrate  the  liver,  is  there  a  secondary  division  into  lobules  (about 
the  fourth  month),  by  which  process  the  primitive  type  gradually 
changes  to  that  characteristic  of  the  adult. 


Nucleus  and 
outer  zone. 


E.  THE  PANCREAS* 

Like  the  liver,  the  pancreas  is  an  accessory  intestinal  gland,  and 
originates  as  a  diverticulum  of  the  intestine.  It  remains  in  perma- 
nent communication  with  the  intestine  by  means  of  its  duct — the 
pancreatic  or  Wirsungian  duct.  The  pancreas  is  composed  of 
numerous  microscopic  lobules, 
surrounded  by  connective  tissue 
which  penetrates  into  the  lob- 
ules and  between  the  alveoli  and 
is  accompanied  by  vessels  and 
nerves.  The  secretory  portion 
of  the  organ  may  be  regarded 
as  a  branched  tubulo-acinal 
gland  with  terminal  alveoli,  the 
latter  forming  the  principal  por- 

,  •  r    ,-,  i       j        r-A  •  Fig.  226. — Transverse  section  through 

tion    Of    the     gland.       The    epi-       aiveoluf  of  frog's  pancreas.     Technic  No. 

thelial  walls  of  the  alveoli  con-      125. 
sist  of  a  number  of  secretoiy 

cells,  whose  appearance  varies  according  to  the  functional  state 
of  the  organ.  The  basilar  portions  of  the  cells  present  a  homo- 
geneous protoplasm,  while  those  parts  of  the  cells  bordering 
upon  the  lumen  are  granular.  The  relation  of  these  zones  to 
each  other  depends  upon  the  physiologic  condition  of  the  gland  ; 
during  starvation  the  internal  or  granular  zone  is  wide  and  promi- 
nent ;  after  moderate  secretion  the  cells  become  as  a  whole  some- 
what smaller,  the  granules  decrease  in  number,  and  the  outer  or 
protoplasmic  zone  increases  in  size.  After  prolonged  secretion 
there  is  an  entire  absence  of  the  granules,  and  the  whole  cell  appar- 
ently consists  of  homogeneous  protoplasm.  It  is  therefore  probable 


266 


THE    DIGESTIVE    ORGANS. 


that  during  a  state  of  rest  peculiar  granules  (zymogen  granules)  are 
formed  at  the  expense  of  the  protoplasm,  and  that  these  granules 
represent  a  preliminary  stage  of  the  finished  secretion.  During  the 
functional  activity  of  the  gland  the  granules  gradually  disappear, 
while  the  fluid  secretion  simultaneously  makes  its  appearance  in  the 
lumen,  although  the  granules  have  as  yet  never  been  observed  in 
the  lumen  itself.  After  secretion  the  cell  grows  again  until  it 
reaches  its  original  size,  only  again  to  begin  the  formation  of  zymo- 
gen granules.  Whether  the  cells  of  the  gland  are  destroyed  or  not 
during  secretion  is  still  a  matter  of  uncertainty. 

An  intermediate  tubule  similar  to  those  of  the  salivary  glands 
connects  with  each  alveolus,  and  then  passes  over  into  a  short  in- 
tralobular  duct.  This  is  lined,  as  in  the  salivary  glands,  with 
columnar  epithelial  cells,  which  are  not,  however  (at  least  in 
man),  striated  at  their  basal  ends.  The  intralobular  ducts  merge 


Centro-acinal 
cell. 


Intermediary 
duct. 


Intralobular  _ 
duct. 


Alveolus. 


_  Intermediary 
duct. 


Fig.  227. — From  section  through  human  pancreas  ;  X  about  200  (sublimate). 


into  excretory  ducts,  which  finally  empty  into  the  pancreatic  duct. 
The  epithelium  of  the  excretory  ducts  is  simple  columnar  in  type. 
Goblet  cells  are  seen  only  in  the  pancreatic  duct. 

In  the  secreting  alveoli  small  protoplasmic,  polygonal,  and  even 
stellate  cells  are  often  seen,  the  so-called  centro-acinal  cells,  or  cells 
of  Langerhans.  The  significance  of  these  structures  is  not  fully 
understood.  Langerhans  himself  supposed  that  they  belonged  to 
the  walls  of  the  excretory  ducts.  This  interpretation  seems  war- 
ranted by  the  fact  that  it  has  been  found  that  the  secreting  cells  of 
the  alveoli  are  directly  joined  to  the  low  cells  of  the  intermediate 
tubules.  When  the  alveoli  lie  closely  packed  together,  the  ad- 
joining intermediate  tubules  fuse  and  are  reduced  to  one  or,  at 
most,  a  few  cells.  As  a  result  a  condition  is  seen  within  the 
alveolar  complexus,  especially  when  the  excretory  ducts  are  in  a 
collapsed  state,  closely  resembling  the  structures  seen  by  Langer- 


THE    PANCREAS. 


26; 


bans.  Peculiar  cells,  wedged  in  here  and  there  between  the  secre- 
tory cells,  but  resting  on  the  membrana  propria,  have  also  been 
observed.  They  undoubtedly  are  sustentacular  cells  of  the  gland 
(cuneate  cells,  Podwyssotzki,  82). 

The  membrana  propria  of  the  alveoli  is  probably  homogenous. 
Immediately  adjoining  it  is  another  delicate  but  firm  membrane, 
consisting  of  fibrils  whose  structure  in  many  respects  resembles  that 
of  the  reticular  fibers  (Gitterfasern)  in  the  liver  and  spleen,  but  which 
are  here  in  relation  to  the  alveoli  (Podwyssotzki,  82). 

In  warm-  and  cold-blooded  animals,  groups  of  cells  differing  in 
arrangement,  size,  and  structure  from  the  secretory  cells,  are  found 
among  the  gland  tubules  and  alveoli  of  the  pancreas  ;  these  are 
known  as  the  intertubular  cell-masses,  or  areas  of  Langerhans.  They 


Outer  zone  of 
a  secretory 
cell. 


Connective 
tissue. 


Larger  gland  — 
duct. 


Centro-acinal 
cell. 


Centro-acinal 
cell. 


Intermediate 
tubule. 

Inner  granular 
zone  of  secre- 
tory cells. 


Fig.  228. — From  section  through  human  pancreas;  X45°  (sublimate). 


consist  of  slightly  granular  cells,  smaller  than  the  secretory  cells 
of  the  alveoli,  arranged  in  the  form  of  anastomosing  trabeculae,  with 
irregular  spaces,  varying  in  size,  separating  the  trabeculae.  Dogiel 
(93)  has  shown  that  in  a  well-preserved  human  pancreas  treated 
by  the  chrome-silver  method,  in  which  the  gland  ducts  even  to 
their  finest  intra-alveolar  branches  were  well  stained,  no  ducts  were 
found  in  the  areas  of  Langerhans.  Such  areas  are,  in  the  human 
pancreas,  usually  separated  from  the  surrounding  gland  tissue  by  a 
small  amount  of  connective  tissue.  They  possess  a  blood  supply, 
consisting  of  relatively  large  capillaries  found  in  the  spaces  formed 
by  the  trabeculae  of  cells  above  mentioned.  The  areas  of  Langer- 
hans have  been  variously  interpreted.  They  have  been  looked 
upon  as  small  areas  of  gland  tissue  in  process  of  degeneration,  or 


268 


THE    DIGESTIVE    ORGANS. 


again  as  areas  of  embryonic  gland  tissue.  From  their  structure 
and  distinct  blood  supply,  and  the  fact  that  no  ducts  have  been 
traced  into  these  areas,  it  seems  probable  that  they  are  small  masses 
of  cells  forming  a  secretion  which  passes  into  the  blood-vessels — in- 
ternal secretion. 

The  blood-vessels   enter  the  gland  with   the    pancreatic  duct, 
divide  into  smaller  branches  in  the  lobules,  and  finally  break  up  into 


Secretory  cell. 


Intermediate 
duct. 


Fig.  229. — Scheme  showing  relation  of  three  adjoining  alveoli  to  excretory  duct, 
illustrating  origin  of  centro-acinal  cells. 


I  > 


Blood  capillary. 


Alveolus  of  gland. 


Area  of  Langer- 
hans. 


Fig.  230. — From  section  of  human  pancreas,  showing  gland  alveoli  surrounding  an  area 

of  Langerhans. 

capillaries  which  encircle  the  secreting  alveoli.  The  meshes  of  the 
capillary  network  are  not  all  of  the  same  size.  In  some  regions 
they  are  so  wide  that  quite  large  areas  of  the  alveoli  are  without 
blood-vessels. 

The  nerves  of  the  pancreas  have  been  investigated  by  Caja)  and 
Sala  (91)  and  Erik  Miiller  (92),  who  find  in  this  gland  large  num- 
bers of  nonmedullated  nerve-fibers,  some  coming  from  sympathetic 


TECHNIC.  269 

ganglion  cells  situated  in  the  pancreas  and  others  entering  from 
without.  The  nonmedullated  nerve-fibers  form  plexuses  surround- 
ing the  excretory  ducts  and  end  in  periacinal  networks.  Fibrils 
from  the  network  about  the  alveoli  were  traced  to  the  secretory 
cells.  A  portion  of  the  nonmedullated  nerves  in  the  pancreas  form 
perivascular  plexuses. 

The  development  of  the  pancreas  is  peculiar  in  that  the  larger 
portion,  together  with  the  duct  of  Santorini,  originates  from  the 
dorsal  intestinal  wall,  and  a  smaller  portion  from  the  ductus  chole- 
dochus.  The  latter  part,  with  its  accessory  pancreatic  duct,  fuses 
with  the  former,  after  which  there  is  a  gradual  retrogression  of  the 
duct  of  Santorini,  so  that  finally  the  entire  secretion  of  the  pancreas 
almost  invariably  flows  into  the  pancreatic  or  Wirsungian  duct. 

TECHNIC 

224.  The  oral  mucous  membrane  may  be  fixed  with  corrosive  sublimate 
or  alcohol,  stained   in  bulk,  and  examined  in  cross-section.      If  special 
structures,  such  as  glands,  nerves,  or  the  distribution  of  mitoses,  are  to 
be  examined,  special  methods  must  be  adopted. 

225.  In  order  to  obtain  a  general  view  of  the  structure  of  the  teeth, 
the  latter  must  be  macerated  and  ground  as  in  the  case  of  bone  (T.  152). 

226.  The  relations  of  the  hard  and  soft  parts  in  undecalcified  teeth 
are  best  studied  by  the  use  of  Koch's  petrifaction  method  (vid.  T.  158). 

227.  The  teeth  may  also  be  examined  in  section,  and  when  decalci- 
'fied  are  treated  as  bone  (vid.  T.  157).    Hydrochloric  acid,  dilute  chromic 
acid,  and  picric  acid  dissolve  the  enamel  prisms,  their  cement-substance 
being  the  first  to  disappear  (von  Ebner,  91). 

228.  The  enamel  of  young  teeth  stains  brown  in  a  solution  of  chromic 
acid  or  its  salts,  and  blackens  in  osmic  acid.    In  the  enamel  cells,  globules 
are  seen,  which  are  stained  in  osmic  acid.      If  longitudinal  sections  of  the 
enamel  be  corroded  with  hydrochloric  acid,  the  cruciform  arrangement 
of  the  enamel  prisms  is  plainly  seen. 

229.  The  fibrils  of  the  dentin  may  be  demonstrated  by  decalcifying 
a  tooth  in  the  fluid  recommended  by  von  Ebner  (T.  157),  the  teeth  of 
young  individuals  being  well  adapted  for   this   purpose.      Occasionally 
carious  teeth  also  show  the  fibrils  plainly.      Corrosion  with  hydrochloric 
acid  produces  the  same  result. 

230.  The  cementum,  especially  that  part  lacking  in  cells,  contains  a 
large  number  of  Sharpey's  fibers. 

231.  The  development  of  the  teeth  is  studied  in  the  embryo  ;  the 
jaw-bone  is  fixed,  decalcified,  and  cut  in  serial  sections.     The  most  con- 
venient material  is  a  sheep  embryo,  which  can  almost  always  be  had  from 
the  slaughter-house. 

232.  To  study  the  taste-buds  of  the  tongue  and  the  relations  which 
their  constituent  cells  bear  to  each  other,   fixation  in  Flemming's  fluid  is 
recommended.     The   orientation   of  the   taste-buds  must  be  very  care- 
fully done,  after  which  exactly  longitudinal  or  transverse  serial  sections 
are  made  (not  thicker  than  5  //)  and  stained  with  safranin -gentian -violet 
(vid.  T.  120). 


2/O  THE    DIGESTIVE    ORGANS. 

233.  The  nerves  in  the  taste -buds  are  brought  out  either  by  Golgi's 
method,  the  methylene-blue  method,  or  by  the  use  of  gold  chlorid.     If 
the  last  be  used  the  procedure  is  as  follows  :     A  papilla  foliata  of  a  rabbit 
is  removed  with  a  sharp  razor  and  placed  for  ten  minutes  in  lemon  juice, 
then  in  gold  chlorid  for  from  three-quarters  of  an  hour  to  one  hour,  after 
which  the  specimen  is  placed  in  water  weakly  acidulated  with  acetic  acid 
(5   drops  to   100  c.c.  of  water)  and  exposed  to  the  light.     As  soon  as 
reduction  has  taken  place  the  specimen  -is  treated  with  alcohol  and  cut  in 
vertical  sections.     These  may  be  treated  for  a  short  time    with  formic 
acid  (in  which  they  swell  slightly),  washed  with  water,  and  mounted  in 
glycerin. 

234.  In  certain  objects,  such  as  the  nictitating  membrane  of  the  frog, 
certain  lobules  of  the  rabbit's  pancreas  (the  latter  being  so  thin  as  to  be 
especially  well  adapted  for  microscopic  examination),  etc.,  the  glandular 
structure  may  be  examined  in  normal  salt  solution. 

235.  Microscopically,  the  glands  present  varying  pictures  according 
to  the  phase  of  secretion  in  which  they  are  fixed.      Specimens  in   the 
different  stages  may  be  obtained  either  by  feeding  and  then  killing  the 
animal  after  a  definite  period,  or  by  irritating  certain  nerves,  or  finally 
by  the  use  of  certain  poisons  especially  adapted  to  this  purpose,  such  as 
atropin  and  pilocarpin.      In  the  rabbit,   for  instance,    i   c.c.  of  a  5^ 
solution  of  pilocarpin  hydrochlorate  or   i  c.c.    of  a  0.5%   solution   of 
atropin  sulphate  is  used  for  each  kilogram   of  the  animal's  weight.      In 
atropin-intoxication  secretion  is  suppressed,  while  in  pilocarpin-poisoning 
it  is  increased.     By  this  method  cells  are  obtained  either  full  of  secretion 
or  containing  no  secretion  at  all. 

236.  Sections    should    be    made    from    carefully   selected    material 
which  has  been  fixed  either  in  Flemming's  solution  or  corrosive  subli- 
mate, although  fixation  with  strong  alcohol  also  gives  instructive  pictures. 

237.  In  preparations  fixed  with  Flemming's  solution  the  crescents  of 
Gianuzzi  stain  somewhat  more  deeply  than  the  remaining  cells  of  the 
alveoli,  and  in  objects  that  have  been  treated  with  alcohol  or  corrosive 
sublimate  and  then  stained  with  hematoxylin  the  crescents  take  on  a  very 
deep  color.     The  intermediate  tubules  of  the  salivary  glands  also  assume 
a  deeper  stain  with  hematoxylin  and  carmin.     The  intralobular  tubes  are 
particularly  well  defined  by  certain  stains,  as  for  instance  when  Congo  red 
is  used  after  staining  with  hematoxylin  ;   other  acid  anilin  stains  may 
also  be  used  (compare  T.  242).     The  intralobular  tubes  of  most  salivary 
glands  (not,  however,  of  the  parotid  of  the  rabbit  nor  of  the  sublingual  of 
the  dog)  are  stained  a  dark -brown  color  (calcareous  reaction)  by  agitat- 
ing small,  fresh  pieces  of  tissue  in  order  to  facilitate  the  entrance  of  air, 
and  then  treating  them  with  a  dilute  aqueous  solution  of  pyrogallic  acid. 
The  stain  persists  for  some  time  in  specimens  preserved  in  alcohol.     Sec- 
tions made  by  free  hand  from  tissues  treated  by  this  method  give  excel- 
lent results  (Merkel,  83). 

238.  Mucin  is  soluble  in  dilute  alkalies,  as  for  instance  lime-water, 
and  may  be  precipitated  from  these  solutions  by  the  addition  of  acetic 
acid,  although  the  precipitate  does  not  redissolve  in  an  excess  of  acetic 
acid ;  mucin  is  also  precipitated  by  alcohol,  but  not  by  heat.      Mucin- 
ogen  does  not  stain  with  hematoxylin,  as  does  mucin.     By  this  latter  test 
a  gland  in  a  state  of  functional  activity  may  be  differentiated  from  one 
at  rest    (R.  Heidenhain,   83).     After  treatment  with  alcohol,   safranin 


TECHNIC.  271 

stains  mucin  orange-yellow.  For  the  demonstration  of  mucin,  more  es- 
pecially in  alcoholic  preparations,  H.  Hoyer  (90)  has  recommended 
thionin  or  its  substitute,  toluidin-blue.  Indeed,  the  basic  anilin  dyes  in 
general  seem  to  have  a  particular  affinity  for  mucin. 

239.  P.   Mayer  (96)   recommends   the   following  two  solutions   for 
the  staining  of  mucin  :    ( i )    Mucicarmin — Carmin   i  gm. ,   aluminium 
chlorid   0.5   gm.,   and  distilled  water  2   c.c.   are    stirred    together  and 
heated  over  a  small  flame  till  the  mixture  becomes  quite  dark.     As  soon 
as  the  mixture  has  attained  the  consistency  of  thick  syrup,  50%  alcohol 
is  added  and  the  whole  transferred  to  a  bottle  in  which  it  is  shaken  after 
the  addition  of  more  alcohol.      Finally,  still  more  50%  alcohol  is  added 
until  the  whole  amounts  to  100  c.c.     Before  using,  this  stock  solution  is 
diluted  tenfold  with  tap-water  rich  in  lime-salts.      (2)    Muchematein  : 
(a)  Aqueous  solution — 0.2  gm.  of  hematein  is  ground  in  a  mortar  con- 
taining a  few  drops  of  glycerin ;  to  this  are  added  o.  i  gm.  aluminium 
chlorid,   40   c.c.   glycerin,   and  60   c.c.   distilled  water.      (<£)  Alcoholic 
solution — 0.2  gm.  hematein,  o.i  gm.  aluminium  chlorid,  TOO  c.c.  70% 
alcohol,  and  i  or  2  drops  of  nitric  acid.     Both  of  these  solutions  are  used 
for  staining  mucin  in  sections  and  thin  membranes.     By  the  use  of  these 
methods  the  mucous  acini  of  mixed  glands  are  shown  with  ease  and  pre- 
cision.     Under   favorable  conditions   the  whole  secretory  and  excretbry 
system  of  the  gland  may  be  brought  out  by  Golgi's  method  (see  this). 

240.  In  order  to  obtain  a  general  structural  view  of  the  esophagus  a 
small  animal  may  be  selected,  in  which  case  small  pieces  of  tissue  are 
fixed  and  imbedded  in  paraffin.      If  a  large  animal  is  used,  the  tissue  is 
imbedded  in  celloidin. 

241.  The  mucous  membrane  of  the  stomach  should  be  fixed  while 
still  fresh  and  warm,  the  best  fixative  for  this  purpose  being  corrosive  sub- 
limate.     Mixtures  of  osmic  acid  are  also  serviceable,  but  fixing  with  cor- 
rosive sublimate  increases  the  staining  power  of  the  tissue.     In  order  to 
preserve  the  stomach  and  intestine  in  a  dilated  condition,  they  should  be 
filled  with  the  fixing  fluid  and  after  ligation  placed  whole  in  the  fixing  agent. 

242.  In  gastric  mucous  membrane  that  has  been  fixed  either  with  cor- 
rosive sublimate  or  alcohol,  the  parietal  cells  are   easily  differentiated 
from  the    chief  cells   by  staining.     The  most  reliable   and    convenient 
method  is  as  follows  :   Sections  fastened  to  the  slide  by  the  water-albumin 
fixative  method  are  stained  with  hematoxylin  and  then  placed  in  a  dilute 
aqueous  solution  of  Congo  red  until  they  assume  a  red  color  (minutes); 
they  are  then  washed  with  dilute  alcohol  until  the  parietal  cells  appear 
red  and  the  chief  cells  bluish  (Stintzing).     Almost  all  acid  anilin  dyes 
have  an  affinity  for  the  parietal  cells  ;   hence  the  red  stains  may  be  com- 
bined with  hematoxylin  and  the  blue  ones  with  carmin.     The  chief  cells 
then  take  the  color  of  the  carmin  or  hematoxylin,  and  the  parietal  cells 
that  of  the  anilins. 

243.  An  accurate  fixation  of  that  portion  of  the  small  intestine  pos- 
sessing villi  is  attended  with  great  difficulty,  since  the  axial  tissue  of  the 
villi  shows  a  tendency  to  retract  from  the  epithelial  layer  surrounding  it 
(the  latter  becoming  fixed  first);  and  as  a  consequence  spaces  are  formed 
at  the  summits  of  the  villi  which  undoubtedly  represent  artefacts.     A 
good  method  is  to  cut  pieces  from  tissue  while  still  warm  and  fix  in  osmic 
acid.      If  portions  of  the  intestine  be  filled  with  alcohol  or  corrosive  sub- 
limate and  thus  dilated,  both  the  glands  and  villi  are  shortened.     The 


2/2  THE    DIGESTIVE    ORGANS. 

methods  above  mentioned  for  staining  mucin  may  be  used  to  stain  the 
goblet  cells.  The  villi  may  also  be  examined  in  a  fresh  condition  in  one 
of  the  indifferent  fluids  (vid.  T.  13).  For  this  purpose  the  intestine  of 
the  mouse  is  especially  well  adapted. 

244.  The  absorption  of  fat  is  best  studied  in  preparations  fixed  in 
osmic  acid,  and  especially  in  those  treated  by  Altmann's  method  (vid. 
T.  124). 

245.  The  technic  for  the  solitary  lymph-follicles  and  Peyer's  patches 
is  the  same  as  that  for  lymph-glands.      For  this  purpose  the  cecum  of  a 
rabbit  or  guinea-pig  is  the  best  material. 

246.  The  nerves  of  the  intestinal  mucous  membrane  are  best  demon- 
strated by  means  of  the  methylene-blue  method  or  Golgi's  method  (vid. 
Technic),  and  the  coarser  filaments  of  Auerbach' sand  Meissner's  plexuses 
may  also  be  stained  by  the  gold  method  (Lowit's  procedure,  T.  182). 
Good  results  are  also  obtained  by  staining  with  hematoxylin  such  speci- 
mens as  have  been  previously  fixed  and  distended  with  alcohol.     The 
plexuses  then  appear  somewhat  darker  than  the  remaining  tissue  of  the 
isolated  mucous  membrane  or  muscular  layer. 

247.  The  arrangement  of  the  liver  lobules  is  best  seen  in  the  pig's 
liver.     In  the  human  liver  and  in  most  domestic  animals  the  lobules  are 
not   sharply  defined,  two  or  three  adjacent  lobules  merging  into  each 
other.     In  the  liver  of  the  fetus,  of  the  new-born,  and  of  children,  the 
lobules  are  seen  indistinctly  or  not  at  all,  although  the  perivascular  spaces 
of  the  blood-vessels  are  better  seen  than  in  the  adult. 

248.  The  liver-cells  are  best  examined  by  treating  small  pieces  of 
tissue  with  i  %  osmic  acid  or  osmic  mixtures ;  in  the  latter  case  subse- 
quent treatment  with  pyroligneous  acid  is  necessary   (T.    18).       Good 
results  can  also  be  obtained  by  fixing  with  corrosive  sublimate  and  stain- 
ing with  hematoxylin  (after  M.  Heidenhain,  T.  65). 

249.  In  order  to  see  the  glycogen   in  the  liver-cells  Ranvier  (89) 
proceeds  as  follows  :   A  dog  is  fed  on  boiled  potatoes  for  two  days,  after 
which  sections  of  its  liver  are  cut  with  a  freezing  microtome  and  examined 
in  iodized  serum  (T.  13).     In  a  short   time   the  glycogen  is  stained  a 
wine-red.     If  the  preparation  be  now  exposed  to  osmic  acid  vapor,  the 
stain  will  remain  fixed  for  from  twenty-four  to  forty -eight  hours.      Glyco- 
gen is  insoluble  in  alcohol  and  ether,  and  stains  a  port  wine-red  in  iodin 
solutions  ;  the  color  disappears  when  the  specimen  is  warmed,  but  returns 
again  on  cooling. 

250.  The  distribution  of  the  hepatic  blood-vessels  is  usually  demon- 
strated by  injection  of  the  portal  vein,  as   the   injection  of  the  hepatic 
artery  does  not,  as  a  rule,  give  such  satisfactory  results. 

251.  The  injection  method  is  also  employed  for  the  demonstration 
of  the   bile   capillaries.      Chrzonszczewsky    recommends    the    following 
so-called    physiologic   autoinjection  :    A    saturated  aqueous  solution  of 
indigo-carmin  is  injected  into  the  external  jugular  vein  three  times  in  the 
course  of  one  and  one-half  hours  (dog  50  c.c.  each  time,  cat  30  c.c., 
full-grown  rabbit  20  c.c.).     The  animal  is  then  killed  and  small  pieces 
of  its  liver  fixed  in  absolute  alcohol  or  in  potassium  chlorid  ;  in  the  latter 
case  a  saturated  solution  of  the  salt  may  be  injected  into  the  blood-ves- 
sels.    A  subsequent  injection  of  the  blood-vessels  with  carmin -gelatin 
may  also  be  employed  and  the  whole  liver  then  hardened  in  alcohol.    By 


TECHNIC.  273 

this  method  the  bile  capillaries  finally  become  filled  with  the  indigo-car  - 
min  by  a  gradual  elimination  of  the  substance  from  the  blood-  and  lymph- 
vessels  and  passage  through  the  cells  into  the  biliary  system,  while  the 
blood-vessels  themselves  are  distended  by  the  carmin-gelatin.  In  the 
frog,  the  demonstration  of  the  biliary  passages  is  more  easily  accomplished 
by  injecting  2  c.c.  of  the  indigo-carmin  solution  into  the  large  lymph- 
sac  and  killing  it  after  a  few  hours.  The  liver  is  then  fixed  in  the  manner 
described  above  and  is  then  ready  for  further  treatment. 

252.  The  bile  passages  may  also  be  injected  directly  through  the 
-hepatic  duct  or  the  ductus  choledochus.      For  this  purpose  it  is  best  to 
use  a  concentrated  aqueous  solution  of  Berlin  blue  (Berlin  blue  that  is 
soluble  in  water).   The  results  obtained  by  this  method  are  not,  however, 
always  satisfactory,  and  even  in  the  best  of  cases  only  the  peripheral  por- 
tions of  the  liver  lobules  are  successfully  injected. 

253.  The  bile  capillaries  may  be   impregnated  with  chrome-silver. 
Fresh  pieces  of  liver  tissue  are  placed  for  two  or  three  days  in  a  potas- 
sium bichromate-osmic  acid  solution   (4  vols.   of  a  3%   bichromate  of 
potassium  solution  and  i  vol.  of  i%  osmic  acid)  and  then  transferred  to 
ao-75%  aqueous  solution  of  silver  nitrate.     After  rinsing  in  distilled 
wrater  the  specimens  are  cut  with  a  razor,  the  sections  again  washed  with 
distilled  water,  placed  for  a  short  time  in  absolute  alcohol,  cleared  in 
xylol,  and    finally  preserved    in  hard  Canada  balsam.     Both    celloidin 
and  paraffin  imbedding  are  admissible,  but  either  process  must  be  hurried, 
as  the  preparation  always  suffers  under  such  treatment.     In  the  finished 
specimen,  the  bile  capillaries  appear  black  by  direct  light. 

254.  Another  method  which  brings  to  view  more  extensive  areas  of  the 
bile  capillaries  is  as  follows  :   A  piece  of  liver  tissue  from  a  freshly  killed 
animal  is  fixed  in  rapidly  ascending  strengths  of  potassium  bichromate 
solution  (from  2%  to  5%).     After  three  weeks  the  specimen  is  placed 
in  a  0.75%  silver  nitrate  solution,  when  after  a  few  days  (very  marked 
after  eight  days)  the  bile  capillaries,  if  examined  in  sections,  will  appear 
black  by  direct  light  (Oppel,  90). 

255.  Sometimes  the  bile  capillaries  are  brought  out  in  preparations 
treated  by  the  method  of  R.  Heidenhain  (T.  85),  although  only  small 
areas  are  colored  and  these  not  constantly.     The  application  of  other 
stains,  as  for  instance  the  method  of  M.   Heidenhain  (T.  65)  following 
the  gold  chlorid  treatment,  often  results  in  the  staining  of  small  areas  of 
bile  capillaries. 

256.  In  all  the  methods  used  for  the  demonstration  of  the  bile  capil- 
laries, whether  physiologic  autoinjection,  direct  injection,  or  impregna- 
tion, the  secretion  vacuoles  of  the  liver-cells  are  clearly  brought  to  view. 

257.  By  treating  pieces  of  liver  tissue  according  to  the  method  of 
Kupffer  (76)  the  connective  tissue  of  the  liver,  especially  the  reticular 
structure    (Gitterfasern),    is  shown.      Fresh  liver  tissue   is  cut  with  the 
double  knife  and  the  thinnest  sections  placed  for  a  short  time  in  a  o.6$> 
sodium  chlorid  solution  or  in  a  0.05%  solution  of  chromic  acid.      From 
this  they  are  transferred  to  a  very  dilute  solution  of  gold  chlorid  (Gerlach) 
(gold chlorid  i  gm.,  hydrochloric  acid  i  c.c.,  water  10  liters),  and  kept 
for  one  to  several  days  in  the  dark  until  they  assume  a  reddish  or  violet 
color.   If  the  staining  has  been  satisfactory  (which  is  by  no  means  always  the 
case),   the  reticular  fibers,  and  occasionally  also  the  stellate  cells,  are 

18 


2/4  THE    DIGESTIVE    ORGANS. 

seen.      Instead  of  the  double  knife  the  freezing  microtome  may  be  used 
and  the  method  continued  as  stated  (Rothe). 

258.  The  reticular  fibers  are  seen  under  more  favorable  conditions  by 
using  the  following  method,  recommended  by  Oppel  (91)  :   Fresh  pieces 
of  tissue  fixed  in  alcohol  are  placed  for  twenty-four  hours  in  a  o.  5  %  aque- 
ous solution  of  yellow  chromate  of  potassium   (larger  pieces  in  stronger 
solutions  up  to  5%),  then  washed  with  a  very  dilute  solution  of  nitrate  of 
silver  (a  few  drops  of  a  0.75%  solution  to  30  c.c.  distilled  water),  and 
transferred  to  a  0.75%  solution  of  silver  nitrate.      In  twenty-four  hours 
the  intralobular  network  surrounding  the  blood  capillaries  will  have  be- 
come stained.     The  best  areas  lie  at  the  periphery  of  the  specimen,  and 
extend    about   i   mm.    into    the    parenchyma.      Free-hand   sections  are 
made,  or  the  specimens  are  quickly  imbedded  in  celloidin  or  paraffin, 
to  be  cut  afterward  by  means  of  the  microtome.     The  same  results  are 
obtained  by  placing  small  fresh  pieces  of  the  tissue  for  two  or  three  days 
in  a  0.5%  chromic  acid  solution  and  then  one  or  two   days  in  a  0.5% 
solution  of  silver  nitrate.     The  further  treatment  is  as  in  the  preceding 
method. 

259.  The  method  of  F.  P.  Mall  (vid.  T.  212)  is  also  employed  in 
the  examination  of  the  hepatic  connective  tissue. 

260.  The  following  method  is  recommended  by  Berkley  for  demon- 
strating the  nerves  of  the  liver  :   Small  pieces  of  liver  tissue  from  0.5  to  i 
mm.  in  breadth  are  placed  in  a  half-saturated  aqueous  solution  of  picric  acid 
for  from  fifteen  to  thirty  minutes,  and  then  in  100  c.c.  of  potassium  bi- 
chromate solution  that  has  been  saturated  in  the  sunlight  and  to  which  16 
c.c.  of  2%  osmic  acid  has  been  added.     The  specimens  now  remain  in 
this  fluid  for  forty-eight  hours  in  a  dark  place,  and  at  a  temperature  of 
25°  C.     After  this  the  tissue  is  treated  with  a  0.25%  to  0.75%  aqueous 
solution  of  silver  nitrate  for  five  or  six  days,  washed  (quick  imbedding 
may  be  employed),  cut,  cleared  in  oil  of  bergamot,  and  mounted  in 
xylol -Canada  balsam. 

261 .  The  cellular  elements  of  the  pancreas  may  be  examined  without 
further  manipulation  in  very  thin  lobules  from  the  rabbit  (Kiihne  and  Lea). 

262.  There  are  various    methods  of   differentiating    the    inner  and 
outer  zones  of  the  cells.      In  sections  of  the  tissue  fixed  in  alcohol,  car- 
min  stains  the  outer  zone  of  the  cells  more  intensely  than  the  inner  (R. 
Heidenhain,  83).      For  the  staining  of  the  inner  zone,  fixation  in  Flem- 
ming's  fluid  is  to  be  recommended,  then  staining  with  safranin,  and  finally 
washing  in  an  alcoholic  solution  of  picric  acid.     The  granules  of  the 
inner  zone  (zymogen  granules)  appear  red.     These  also  stain  red  with 
the  Biondi-Ehrlich  mixture   (T.  78).     The  simplest  and  most   precise 
method    of   demonstrating   the    zymogen  granules    is    that  of   Altmann 
(T.  124).     The  secretory  and  excretory  ducts  of  the  pancreas  are  shown, 
as   in   the  case   of  the    salivary   glands,    by  the  chrome -silver   method 
(compare  T.  253), 


THE    LARYNX. 


275 


IV.  ORGANS  OF  RESPIRATION. 

A.  THE  LARYNX. 

THE  greater  portion  of  the  laryngeal  mucous  membrane  is  cov- 
ered by  a  stratified  columnar  ciliated  epithelium  containing  goblet 
cells,  and  resting  on  a  thick  basement  membrane.  The  epithelium 
covering  the  free  margin  of  the  epiglottis,  the  true  vocal  cords,  and 


Glands  in  false 
vocal  cord. 


Stratified  pavement    »^ 
epithelium  of  true    \ 
vocal  cord.  \ 


Stratified  ciliated  col- 
umnar epithelium. 


Glands. 


Muscle. 


Fig-  231. — Vertical  section  through  the  mucous  membrane  of  the  human  larynx  ;  X5- 


2/6  ORGANS    OF    RESPIRATION. 

part  of  the  arytenoid  cartilage  as  far  as  the  cavity  between  these 
cartilages,  is  of  the  stratified  squamous  variety,  and  is  provided  with 
connective-tissue  papillae.  The  mucosa  contains  many  elastic  fibers, 
and  is  rather  firmly  connected  with  the  structures  underneath  it,  but 
is  somewhat  more  loosely  connected  in  the  regions  supplied  with 
squamous  epithelium.  In  it  are  found  branched  tubulo-acinal 
glands,  which  may  be  single  or  arranged  in  groups.  These  are  found 
at  the  free  posterior  portion  of  the  epiglottis,  in  the  region  of  the 
latter's  point  of  attachment — i.  e.,  in  the  so-called  cushion  of  the 
epiglottis.  Larger  collections  of  glands  are  found  in  the  false  vocal 
cords,  and  on  the  cartilages  of  Wrisberg  (cuneiform  cartilages),  which 
appear  almost  imbedded  in  the  glandular  tissue.  In  the  remaining 
parts  of  the  larynx  glands  are  found  only  at  isolated  points.  The 
true  vocal  cords  have  no  glands. 

The  cartilages  of  the  larynx  are  of  the  hyaline  variety,  with  the 
exception  of  the  epiglottis,  the  cartilages  of  Santorini  (the  latter 
are  derivatives  of  the  epiglottis,  Goppert),  the  cuneiform  cartilages, 
the  processus  vocalis,  and  a  small  portion  of  the  thyroid  at  the 
points  of  attachment  of  the  vocal  cords,  which  consist  of  elastic  car- 
tilage. 

The  vascular  supply  of  the  larynx  is  arranged  in  three  super- 
imposed networks  of  blood-vessels.  The  capillaries  are  very  fine, 
and  lie  directly  beneath  the  epithelium.  The  lymphatic  network  is 
arranged  in  two  layers,  the  superficial  being  very  fine  and  di- 
rectly beneath  the  network  of  blood  capillaries. 

The  nerves  of  the  laryngeal  mucous  membrane  will  be  de- 
scribed in  connection  with  those  found  in  the  trachea. 


B.  THE  TRACHEA. 

The  trachea  is  lined  by  a  stratified  ciliated  columnar  epithelium 
containing  goblet  cells  and  resting  on  a  well-developed  basement 
membrane.  The  mucosa  is  rich  in  elastic  tissue.  In  the  super- 
ficial portion  of  the  mucosa  the  elastic  fibers  form  dense  strands, 
which  usually  take  a  longitudinal  direction.  The  deeper  layer  of 
the  mucosa  is  more  loosely  constructed,  and  passes  over  into  the 
perichondrium  of  the  semilunar  cartilages  of  the  trachea  without 
any  sharp  line  of  demarcation.  Numerous  leucocytes  are  scattered 
throughout  the  mucosa,  and  are  also  frequently  found  in  the  epi- 
thelium. Connecting  the  free  ends  of  the  semilunar  cartilages, 
which  are  of  the  hyaline  variety,  are  found  bundles  of  nonstriated 
muscle  tissue,  the  direction  of  which  is  nearly  transverse. 

The  trachea  contains  numerous  branched  tubulo-acinal  glands 
of  the  mucous  variety  containing  here  and  there  crescents  of 
Gianuzzi.  The  glands  are  especially  numerous  where  the  tracheal 
wall  is  devoid  of  cartilage. 

The  larynx  and  trachea  receive  their  nerve  supply  from  sensory 


THE   BRONCHI,  THEIR  BRANCHES,  AND  THE    BRONCHIOLES. 

nerve-fibers  and  sympathetic  neurones.  These  have  been  described 
by  Ploschko  (97)  working  in  Arnstein's  laboratory.  According  to 
this  observer,  the  sensory  fibers  divide  in  the  mucosa,  forming  sub- 
epithelial  plexuses  from  which  fibrils  are  given  off  which  enter  the 
epithelium  of  the  larynx  and  trachea  and,  after  further  division,  end 
on  the  epithelial  cells  in  small  nodules,  or  small  clusters  of  nodules. 
In  the  trachea  of  the  dog,  such  fibrils  were  traced  to  the  ciliary 
border  of  the  columnar  ciliated  cells  before  terminating.  Numerous 
sympathetic  ganglia  are  found  in  the  larynx  and  trachea.  In  the 
latter  they  are  especially  numerous  in  the  posterior  wall.  The 
neuraxes  of  the  sympathetic  neurones  forming  these  ganglia  were 
traced  to  the  nonstriated  muscular  tissue  of  the  trachea.  The  cell- 
bodies  of  these  sympathetic  neurones  are  surrounded  by  end-baskets 
of  small  medullated  fibers  terminating  in  the  ganglia.  Medullated 


Fig.  232. — From  longitudinal  section  of  human  trachea,  stained  in  orcein. 

nerve -fibers,  ending  in  the  musculature  of  the  trachea  in  peculiar 
end-brushes,  were  also  described  by  Ploschko. 

C  THE  BRONCHI,  THEIR  BRANCHES,  AND  THE 
BRONCHIOLES. 

The  primary  bronchi  and  their  branches  show  the  same  general 
structure  as  the  trachea.  The  epithelium  of  the  bronchi  of  medium 
size  (up  to  0.5  mm.  in  diameter)  consists  of  a  ciliated  epithelium 
having  three  strata  of  nuclei.  Kolliker  (81)  distinguishes  a  deep 
layer  of  basilar  cells,  a  middle  layer  of  replacing  cells,  and  a  super- 
ficial zone  consisting  of  ciliate  and  goblet  cells.  The  number 
of  the  last  varies  greatly.  Glands  are  found  only  in  bronchial 
twigs  that  are  not  less  than  I  mm.  in  diameter ;  as  in  the  trachea, 
they  are  branched  tubulo-acinous  glands  of  the  mucous  variety. 


278 


ORGANS    OF    RESPIRATION. 


In  these  structures  the  mucosa  contains  a  large  number  of  elastic 
fibers,  the  greater  part  of  which  have  a  longitudinal  direction. 
Furthermore,  numerous  lymph-cells  are  found,  and  here  and  there 
a  lymph-nodule.  The  muscularis  presents,  as  a  rule,  circular  fibers, 
which  do  not,  however,  form  a  continuous  layer.  The  cartilaginous 
framework  here  no  longer  consists  of  symmetrically  arranged 
rings,  but  of  irregular  platelets,  which  are  absent  in  bronchial 
twigs  less  than  0.85  mm.  in  diameter. 

The   smaller  bronchi   subdivide  into  still  finer  tubules  of  less 
than  0.5  mm.  in   diameter  (bronchioles),  which  contain  neither  car- 


Stratified  cili- 

ated  columnar 

epithelium. 

•&3£ Elastic   fibers, 

$£!&?•  cut  trans- 

i^^h-r          versely. 


;*  ;  v*'-:°:.~   v>y-:.«. 

v^^'S^i 

V-:IV^"^!.r 


:  *•;-. •'.•I.r-'..-. 

••*%    "  ,  **     J°    --«* —   Cartilage. 
.  :-•  a4-     A    0?e%e 


Fig-  233- — Transverse  section  through  human  bronchus  ;  X  27- 

tilage  nor  glands.  The  stratum  proprium,  as  well  as  the  external 
connective-tissue  sheath,  becomes  very  thin  ;  and  the  epithelium 
now  consists  of  but  one  layer,  but  is  still  ciliated. 


RESPIRATORY    BRONCHIOLES    AND    INFUNDIBULA. 


279 


D.  THE  RESPIRATORY  BRONCHIOLES,  ALVEOLAR 
DUCTS,  AND  INFUNDIBULA* 

The   bronchioles  are  continued  as  the  respiratory  bronchioles. 


-jj .  -  -  -  Artery. 


—  Lung  tissue. 


_l Bronchiole. 


- —  Lung  tissue. 


Alveolar  duct.  — 


Fig-  235- 
Figs.  234  and  235.— Two  sections  of  cat's  lung  :  Fig.  234,  X  52  J  Fi£-  235»  X  35- 

The  epithelium  of  the  latter  is  ciliated  in  patches,  but  ultimately  be- 
comes nonciliated,  and  assumes  the  character  of  the  respiratory  epi- 


280 


ORGANS    OF    RESPIRATION. 


thelium.  (See  below.)  The  fine  tubular  segments  of  the  respiratory 
passages,  lined  by  an  epithelium  which  marks  the  transition  from  the 
mixed  to  the  respiratory  epithelium,  are  known  as  the  alveolar 
ducts.  The  muscle-fibers  may  be  traced  as  far  as  these  segments, 
where  they  are  lost.  Both  in  the  walls  of  the  respiratory  bron- 
chioles and  along  the  alveolar  ducts  there  occur  diverticula  called 
alveoli. 

Each  alveolar  duct  is  continuous  with  a  so-called  infundibulum. 


Section  of  al 

veolus  of 
lung. 


Respiratory 

(•  bronchiole 

with  two 
kinds  of 
epithelium. 


Fig.  236. — Internal  surface  of  a  human  respiratory  bronchiole,  treated  with  silver 
nitrate  ;  X  234  (after  Kolliker). 

The  general  shape  of  the  latter  is  conical,  the  base  of  the  cone  be- 
ing turned  away  from  the  duct.  Numerous  diverticula  are  present 
in  the  walls  of  the  infundibula,  known  as  the  air-sacs  or  alveoli  of 
the  lung.  The  epithelium  of  the  infundibulum  (i  I  p,  to  1 5  /*  in  diam- 
eter) and  of  its  alveoli  (the  so-called  respiratory  epithelium)  con- 
sists of  two  varieties  of  cells  (F.  E.  Schulze) — smaller  nucleated 
elements  and  larger  nonnucleated  platelets  (the  latter  derived  very 
probably  from  the  former).  The  arrangement  of  the  epithelial  cells 


RESPIRATORY    BRONCHIOLES    AND    INFUNDIBULA.  28 1 

is  generally  such  that  the  nonnucleated  platelets  rest  directly  upon 
the  blood  capillaries,  while  nucleated  cells  lie  between  them.  The 
basement  membrane  beneath  the  epithelium  of  the  respiratory  pas- 
sages gradually  becomes  thinner  as  it  approaches  the  infundibula, 
and  in  the  latter  is  scarcely  to  be  seen. 

In  amphibia  the  epithelium  of  the  alveoli  consists  of  cells,  of  which 
the  portion  containing  the  nucleus  forms  a  broad  cylindric  base  ;  from  the 
free  end  of  each  cell  a  lateral  process  extends  over  the  adjoining  capillary 
to  meet  a  similar  process  from  the  neighboring  cell.  When  viewed 
from  above,  the  basal  portion  of  the  cell  appears  dark  and  granular,  while 
the  processes  are  clear  and  transparent.  These  cells,  together  with  their 
prolongations,  are  about  50  /*  in  diameter.  The  surface  view  greatly  re- 
sembles that  of  the  human  respiratory  epithelium  (Duval,  Oppel,  89]. 


Nonnucleated  epi- 
thelial cell. 


Nucleated  epithelial 

cell. 


Fig-  237- — Inner  surface  of  human  alveolus  treated  with  silver  nitrate,  showing  respira- 
tory epithelium  ;   X  24°  (after  Kolliker). 

The  walls  of  the  infundibulum  and  its  alveoli  are  encircled  by 
very  delicate  elastic  fibers. 

The  lung  tissue  is  arranged  in  small  lobules,  which  form  defi- 
nite units  in  its  anatomy  and  pathology  (Councilmann,  1900).  These 
lobules  have  a  diameter  of  from  i  to  3  cm.  in  the  adult,  and  from 
0.5  to  1.5  cm.  in  the  child  from  two  to  eight  years  old.  They  are 
of  pyramidal  shape,  the  apex  of  the  lobule  being  formed  by  a  small 
bronchus.  They  are  separated  from  one  another  by  a  small  amount 
of  interlobular  fibrous  tissue.  The  small  bronchus  entering  the 
apex  of  each  lobule  divides  within  the  lobule  several  times,  each 
bronchiole  becoming  a  respiratory  bronchiole,  alveolar  duct,  and 
infundibulum,  with  alveoli  or  air-sacs  associated  with  them. 

The  visceral  and  the  parietal  layers  of  the  pleura  consist  of  a 
layer  of  fibro-elastic  tissue  covered  by  a  layer  of  mesothelium. 

The  blood-vessels  of  the   lung   have  been  described  by  Miller 


282 


ORGANS    OF    RESPIRATION. 


(93)  working  under  Mall's  direction.  His  account  is  closely  fol- 
lowed in  the  following  description  :  The  pulmonary  artery  follows 
closely  the  bronchi  through  their  entire  length.  An  arterial  branch 
enters  each  lobule  of  the  lung  at  its  apex  in  close  proximity  to  the 
bronchus.  After  entering  the  lobule  the  artery  divides  quite  ab- 
ruptly, a  branch  going  to  each  infundibulum  ;  from  these  branches 
the  small  arterioles  arise  which  supply  the  alveoli  of  the  lung. 
"  On  reaching  the  air-sac  the  artery  breaks  up  into  small  radicals 
which  pass  to  the  central  side  of  the  sac  in  the  sulci  between  the 
air-cells,  and  are  finally  lost  in  the  rich  system  of  capillaries  to  which 
they  give  rise.  This  network  surrounds  the  whole  air-sac  and 
communicates  freely  with  that  of  the  surrounding  sacs."  This 
capillary  network  is  exceedingly  fine  and  is  sunken  into  the  epi- 
thelium of  the  air-sacs  so  that  between  the  epithelium  and  the  capil- 
lary there  is  only  the  extremely 
delicate  basement  membrane. 
The  infundibula,  the  alveolar 
ducts  and  their  alveoli,  and  the 
alveoli  of  the  respiratory  bron- 
chioles are  supplied  with  similar 
capillary  networks.  The  veins 
collecting  the  blood  from  the 
lobules  lie  at  the  periphery  of  the 
lobules  in  the  interlobular  con- 
nective tissue,  and  are  as  far  dis- 
tant from  the  intralobular  arteries 
as  possible.  These  veins  unite  to 
form  the  larger  pulmonary  veins. 
The  bronchi,  both  large  and 
small,  as  well  as  the  bronchioles, 
derive  their  blood  supply  from 
the  bronchial  arteries,  which  also 
partly  supply  the  lung  itself. 
Capillaries  derived  from  these  ar- 
teries surround  the  bronchial  system,  their  caliber  varying  according 
to  the  structure  they  supply — finer  and  more  closely  arranged  in  the 
mucous  membrane,  and  coarser  in  the  connective-tissue  walls.  In 
the  neighborhood  of  the  terminal  bronchial  tubes  the  capillary  nets 
anastomose  freely  with  those  of  the  respiratory  capillary  system. 
From  the  capillaries  of  the  bronchial  arteries,  veins  are  formed  which 
empty  either  into  the  bronchial  veins  or  into  the  branches  of  the 
pulmonary  veins. 

The  lymphatics  of  the  lung  originate  between  the  alveoli.  They 
form  two  sets  of  vessels  (Councilmann,  1900) — the  one  found  in  the 
interlobular  connective  tissue,  which  communicates  with  lymph- 
vessels  in  the  pleura,  forming  a  rich  plexus,  terminating  in  several 
lymphatic  vessels,  provided  with  valves,  which  end  in  the  lymph- 
glands  at  the  root  of  the  lung,  and  "  a  central  set  which  accompa- 


Fig.  238. — Scheme  of  the  respiratory 
epithelium  in  amphibia  :  The  upper  figure 
gives  a  surface  view  :  b,  Basilar  portion  ;  a, 
the  thin  process.  The  lower  figure  is  a  sec- 
tion :  a,  Respiratory  epithelial  cell ;  £,  blood- 
vessel ;  c,  connective  tissue  around  the  al- 
veoli. 


RESPIRATORY    BRONCHIOLES    AND    INFUNDIBULA. 


283 


nies  the  pulmonary  artery  and  passes  directly  into  the  bronchial 
glands  at  the  hilum  of  the  lung." 

Accompanying  the  bronchi  and  bronchial  arteries  are  found 
numerous  nerve-fibers,  of  the  nonmedullated  and  medullated  varie- 
ties, arranged  in  bundles  of  varying  size,  in  the  course  of  which  are 


Fig-  239- — From  section  of  human  lung  stained  in  orcein,  showing  the  elastic  fibers  sur- 
rounding the  alveoli. 


Blood  capillaries 
seen  in  surface 


-  -  f*-  —  Alveolus  in  cross- 

/  section. 

. 
Fig.  240. — Section  through  injected  lung  of  rabbit. 

found  sympathetic  ganglia.  Berkley  (94),  who  has  studied  the  dis- 
tribution of  the  nerves  of  the  lung  with  the  chrome-silver  method, 
finds  that  in  the  external  fibrous  layer  of  the  bronchi  is  found  a 
plexus  of  very  fine  and  of  coarser  fibers,  from  which  branches  are 


284 


ORGANS    OF    RESPIRATION. 


given  off  which  end  in  the  muscle  tissue  of  the  bronchi,  and  others 
which  pass  through  this  layer  to  form,  after  further  division,  a  sub- 
epithelial  plexus  from  which  fibrils  may  be  traced  into  the  connec- 
tive-tissue folds  in  the  larger  bronchi  and  between  the  bases  of  the 
epithelial  cells  in  the  smaller  bronchi  and  bronchioles.  Some  few 
fibrils  were  traced  between  alveoli  situated  near  bronchi,  "  termi- 
nating, apparently,  immediately  beneath  the  pavement  epithelium  in 
an  elongated  or  rounded  minute  bulb  ;  "  these  may,  however,  repre- 
sent endings  on  nonstriated  muscle  tissue.  The  bronchial  arteries 
have  an  exceedingly  rich  nerve  supply. 


K  THE  THYROID  GLAND. 

The  thyroid  gland  is  developed  from  three  sources  :   Its  middle 
portion,  the  isthmus  of  the  gland,  originates  as  a  diverticulum  of 


Lumen  of  follicle. 
Connective  tissue. 

Epithelium  of  follicle. 


Fig.  241. — From  section  through  thyroid  gland  of  child. 

the  pharyngeal  epithelium,  from  what  is  later  the  foramen  caecum  of 
the  tongue  ;  both  lateral  portions,  the  right  and  left  lobes,  are  formed 
from  a  complicated  metamorphosis  of  the  epithelium  of  the  fourth 
visceral  pouch.  These  various  parts  unite  in  man  into  one,  so  that 
in  the  adult  the  structure  of  the  organ  is  continuous.  The  thyroid 
gland  consists  of  numerous  noncommunicating  acini  or  follicles  of 
various  sizes  lined  by  a  nearly  cubic  epithelium  ;  the  lobules  are 
separated  from  each  other  by  a  highly  vascularized  connective  tissue, 
continuous  with  the  firm  connective-tissue  sheath  surrounding  the 
whole  gland.  The  follicles  are  either  round,  polyhedral,  or  tubular, 
and  are  occasionally  branched  (Streiff ).  At  an  early  stage  the  acini 
are  found  to  contain  a  substance  known  as  "  colloid "  material 
(vid.  Technic). 

Langendorff  has  shown  (vid.  Technic)  that  two  varieties  of  cells 
exist  in  the  acini  of  the  thyroid  body — the  chief  cells  and  colloid 


THE    THYROID    GLAND.  28$ 

cells.  Those  of  the  first  variety  apparently  change  into  colloid 
cells,  while  the  latter  secrete  the  colloid  substance.  During  the 
formation  of  this  material  the  colloid  cells  become  lower,  and  their 
entire  contents,  including  the  nuclei,  change  into  the  colloid  mass. 
Hiirthle  distinguished  two  processes  of  colloid  secretion  ;  in  the  one 
the  cells  remain  intact,  in  the  other  they  are  destroyed.  He  claims 
that  the  colloid  cells  of  LangendorfT  participate  in  the  former  pro- 
cess, while  in  the  latter  they  are  first  modified  (flattened)  and  then 
changed  into  the  colloid  substance.  The  colloid  material  may 
enter  the  lymph-channels,  either  directly  by  a  rupture  of  the  acini, 
or  indirectly  by  a  percolation  of  the  substance  into  the  intercellular 
clefts,  whence  it  is  carried  into  the  larger  lymphatics. 

Anderson  (91)  and  Berkley  (94)  have  studied  the  distribution 
of  the  nerve-fibers  of  the  thyroid  gland  with  the  chrome-silver 
method ;  the  account  given  by  the  latter  is  the  more  complete  and 
will  be  followed  here.  The  nonmedullated  nerves  entering  the  gland 
form  plexuses  about  the  larger  arteries,  which  are  less  dense  around 
the  smaller  arterial  branches.  Some  of  these  nerve-fibers  are  vascular 
nerves  and  end  on  the  vessels  ;  others  form  perifollicular  meshes 
surrounding  the  follicles  of  the  gland.  From  the  network  of  nerve- 
fibers  about  the  follicles,  Berkley  was  able  to  trace  fine  nerve  fila- 
ments which  seemed  to  terminate  in  end-knobs  on  or  between  the 
epithelial  cells  lining  the  follicles.  Even  in  the  best  stained  prepa- 
rations, however,  not  nearly  all  the  follicular  cells  possess  such  a 
nerve  termination.  In  methylene-blue  preparations  of  the  thyroid 
gland  (Dr.  De  Witt)  some  few  medullated  fibers  were  found  in  the 
nerve  plexus  surrounding  the  vessels.  In  a  number  of  preparations 
these  were  traced  to  telodendria  situated  in  the  adventitia  of  the 
vessels,  showing  that  at  least  a  portion  of  these  medullated  nerves 
are  sensory  nerves  ending  in  the  walls  of  the  vessels. 


PARATHYROID  GLANDS. 

Small  glandular  structures  found  on  the  posterior  surfaces  of  the 
lateral  lobes  of  the  thyroid  were  discovered  by  Sandstrom  in  1880. 
They  are  surrounded  by  a  thin  connective-tissue  capsule  and  divided 
into  small  imperfectly  developed  lobules  by  a  few  thin  fibrous-tissue 
septa  or  trabeculae,  which  support  the  larger  vessels.  The  epithelial 
portions  of  these  structures  consist  of  relatively  large  cells  and  capil- 
lary spaces.  According  to  Schaper  (95),  who  has  recently  subjected 
these  structures  to  a  careful  investigation,  the  epithelial  cells  have 
a  diameter  which  varies  from  10  //to  12  //,  possessing  nuclei  4  fj. 
in  diameter.  These  cells  are  of  polygonal  shape  and  have  a  thin 
cell-membrane,  a  slightly  granular  protoplasm,  and  a  nucleus  pre- 
senting a  delicate  chromatic  network.  The  cells  are  arranged  either 
in  larger  or  smaller  clusters  or,  in  some  instances,  in  anastomosing 
trabeculae  or  columns,  consisting  either  of  a  single  row  or  of  several 
rows  of  cells.  Between  the  clusters  or  columns  of  cells  are  found  rela- 


286 


ORGANS    OF    RESPIRATION. 


tively  large  capillaries,  the  endothelial  lining  of  which  rests  directly 
on  the  epithelial  cells.  Connective-tissue  fibrils  do  not,  as  a  rule, 
follow  the  capillaries  between  the  cell-masses.  The  structure  of 
the  parathyroid  resembles  in  many  respects  that  of  certain  embryonic 
stages  of  the  thyroid,  and  it  has  been  suggested  that  these  bodies 
represent  small  masses  of  thyroid  gland  tissue,  retaining  their  em- 
bryonic structure.  Schaper  has  observed  parathyroid  tissue,  the 
cells  of  which  were  here  and  there  arranged  in  the  form  of  small 
follicles,  some  of  which  contained  colloid  substance.  Such  obser- 
vations lend  credence  to  the  view  regarding  the  parathyroid  as  an 
embryonic  structure.  Whether  in  this  stage  they  form  a  special 
secretion  has  not  been  fully  determined.  (See  Schaper,  95.) 


9  «r-/3    .•*' 

Wffid$. 

X-4:i:Kn»  MM 


V" 

53>N, 


Fig.  242. — From  parathyroid  of  man. 


TECHNIC 

263.  For  the  demonstration  of  the  larynx  and  trachea,  young  and 
healthy  subjects  should  be  selected.      Pieces  of  the  mucous  membrane  or 
the  whole  organ  should  be  immersed  in  a   fresh  condition.      Sections 
through  the  entire  organ  present  only  a  general  structural  view ;  but  if 
a  close  examination  of  accurately  fixed  mucous  membrane  be  desired,  the 
latter  should  be  removed  with  a  razor   before  sectioning  and   treated 
separately. 

264.  Chromic-osmic  acid  mixtures  are  recommended  as  fixing  agents, 
and  safranin  as  a  stain.     Besides  the  nuclear  differentiation,  the  goblet  cells 
stain  brown,  and  the  elastic  network  of  the  stratum  proprium  and  the 
submucosa  a  reddish -brown. 

For  examining  the  epithelium,  isolation  methods  are  employed,  such 
as  the  YZ  alcohol  of  Ranvier  (T.  128). 

265.  The  examination  of  the  respiratory  epithelium  is  attended  with 
peculiar   difficulty ;    it   is,    perhaps,    best   accomplished   by  injecting   a 
0.5%    solution  of  silver  nitrate  into  the  bronchus  until  the  lumen  is 
completely  filled,  and  then  placing  the  whole  in  a  0.5%  solution  of  the 
same  salt.     After  a  few  hours,  wash  with  distilled  water  and  transfer  to 


THE    URINARY    ORGANS.  28/ 

70%  alcohol.  Thick  sections  are  now  cut  and  portions  of  the  respiratory 
passages  examined  ;  the  silver  lines  represent  the  margins  of  the  epithe- 
lial cells.  Such  sections  should  not  be  fastened  to  the  slide  with  albumen, 
as  the  latter  soon  darkens  and  blurs  the  picture.  These  specimens  may 
also  be  stained. 

266.  For  the  elastic  fibers,  especially  those  of  the  alveoli,  fixation  in 
Miiller's  fluid  (T.  27)  or  in  alcohol  and  staining  with  orcein  is  a  good 
method.      Fresh  pieces  of  lung  tissue  treated  with  potassium    hydrate 
show  numerous  isolated  elastic  fibers. 

267.  Pulmonary  tissue   may  be  treated  by  Golgi's   method,   which 
brings  out  a  reticular  connective-tissue  structure  in  the  vessels  and  alveoli 
(vid.  T.  252,  Oppel). 

268.  The  pulmonary  vessels  may  be  injected  with  comparative  ease. 

269.  The  thyroid  gland  is  best  fixed  in  Flemming's  solution ;  it  is 
then  stained  with  M.  Heidenhain's  hematoxylin  solution  or,  better  still, 
with  the  Ehrlich-Biondi  mixture  which  differentiates  the  chief  from  the 
colloid  cells  ;   the  former  do  not  stain  at  all,  while  the  latter  appear  red 
with  a  green  nucleus  (Langendorff).      The  colloid  substance  of  the  thy- 
roid gland  does  not  cloud  in  alcohol  or  chromic  acid,  nor  does  it  coagu- 
late in  acetic  acid,  but  swells  in  the  latter;    33%    potassium  hydrate 
hardly  causes  the  colloid  material  to  swell  at  all,  though  in  weaker  solu- 
tions it  dissolves  after  a  long  time. 


V.  THE  GENITOURINARY   ORGANS. 

A.  THE  URINARY  ORGANS. 

J.  THE  KIDNEY. 

THE  kidney  is  a  branched  tubular  lobular  gland,  which  in  man 
consists  of  from  ten  to  fifteen  nearly  equal  divisions  of  pyramidal 
shape  known  as  the  renal  lobes.  The  apex  of  each  pyramid  (the 
Malpighian  pyramid)  projects  into  the  pelvis  of  the  kidney.  The 
kidney  is  surrounded 
by  a  thin  but  firm  cap- 
sule consisting  of  fib- 
rous connective  tissue  a  \ ff3^  (  ~** tiPTtlMliilLi  iniiiiilfo  Artery, 
containing  a  few  elas- 
tic fibers  and,  in  its 
deeper  portion,  a  thin 
layer  of  nonstriated 

i          11  Fig.  243. — Kidney  of  new-born  infant,  showing  a 

1S*    m  distinct  separation  into  reniculi ;  natural   size.     At  a  is 

The  Secreting  por-       seen  the  consolidation  of  two  adjacent  reniculi. 

tion  is  composed  of  a 

large  number  of  tubules  twisted  and  bent  in  a  definite  and  typical 
manner,  the  urimferous  tubules.  In  each  one  of  these  tubules  we 
distinguish  the  following  segments  :  (i)  Bowman's  capsule,  or  the 
ampulla,  surrounding  a  spheric  plexus  of  capillaries,  tJic  glomerulus, 
which,  with  the  capsule  of  Bowman,  forms  a  Malpighian  corpuscle  ; 


288 


THE    GENITOURINARY    ORGANS. 


(2)  a  proximal  convoluted  portion ;  (3)  a  U-shaped  portion,  con- 
sisting of  straight  descending  and  ascending  limbs  and  the  loop 
of  Henle ;  (4)  a  distal  convoluted  portion  or  intercalated  portion ; 
and  (5)  an  arched  collecting  portion  ;  from  the  confluence  of  a  num- 
ber of  these  are  formed  the  larger  straight  collecting  tubules,  which, 
turn,  finally  unite  to  form  the  papillary  ducts  or  tubules  of 


in 


Bellini,  which  pass  through  the  renal  papillae  and  empty  into  the 
renal  pelvis.  Besides  the  uriniferous  tubules  the  kidney  con- 
tains a  complicated  vascular  system,  a  small  amount  of  connective 
tissue,  etc. 


.  c 


Fig.  244. — Isolated  uriniferous  tubules  :  A  and  B,  from  mouse  ;  C,  from  turtle. 
In  all  three  figures  a  represents  the  Malpighian  corpuscle  ;  b,  the  proximal  convoluted 
tubule;  c,  the  descending  limb  of  Henle' s  loop;  d,  Henle' s  loop;  e,  the  straight  col- 
lecting tubule  ;  /,  the  arched  collecting  tubule. 

In  a  longitudinal  median  section  the  kidney  is  seen  to  be  com- 
posed of  two  substances, — the  one,  the  medullary  substance,  pos- 
sessing relatively  few  blood  capillaries  and  containing  straight 
collecting  tubules  and  the  loops  of  Henle  ;  the  other,  the  cortical 
substance ,  richer  in  blood-vessels,  and  containing  principally  the 
Malpighian  corpuscles  and  the  proximal  and  distal  convoluted  tu- 
bules. In  each  renal  lobe  we  find  these  two  substances  distributed 
as  follows  :  The  Malpighian  pyramid  consists  entirely  of  medullary 
substance,  which  sends  out  a  large  number  of  processes,  the  mcdul- 


THE    URINARY    ORGANS. 


289 


lary  rays,  or  pyramids  of  Ferrein,  toward  the  surface  of  the  kidney. 
The  latter  do  not,  however,  quite  reach  the  surface,  but  terminate  at 
a  certain  distance  below  it ;  they  are  formed  by  collecting  tubules 
which  extend  beyond  the  medullary  substance.  The  entire  remain- 
ing portion  of  the  kidney  is  composed  of  cortical  substance  ;  be- 
tween the  medullary  rays  it  forms  the  cortical  processes,  and  at  the 
periphery  of  the  kidney,  where  the  medullary  rays  are  absent,  the 
cortical  labyrinth.  Those  portions  of  the  cortical  substance  sep- 
arating the  Malpighian  pyramids  are  known  as  the  columns  of 
Bertini,  or  septa  rents. 


Column  of  Ber-  _          / 
tini.  " 


Medullary  --' 
rays. 


Malpighian 
pyramid. 

Lobule  of  adi- 
pose tissue. 


Blood-vessel.    V- 


Fig.  245. — Median  longitudinal  section  of  adult  human  kidney  ;  nine-tenths  natural 
size.  In  the  peripheral  portion  the  limits  between  its  renal  lobes  are  no  longer  recogniz- 
able. 


The  various  segments  of  the  uriniferous  tubule  are  characterized 
by  their  shape  and  size  and  by  their  epithelial  lining. 

The  Malpighian  corpuscle  has  a  diameter  of  from  120^  to  220  ;/. 
The  capsule  surrounding  the  glomerulus  consists  of  two  layers, 
which  are  to  be  distinguished  from  each  other  when  its  relation  to 
the  glomerulus  is  taken  into  consideration.  The  capsule  forms  a 
double-walled  membrane  around  the  glomerulus ;  a  condition 
which  is  easily  understood  by  imagining  an  invagination  of  the 
19 


290  THE    GENITOURINARY    ORGANS. 

glomerulus  into  the  hollow  capsule.  Between  the  inner  wall  cov- 
ering the  surface  of  the  glomerulus  (glomerular  epithelium)  and  the 
outer  wall  (Bowman's  capsule)  there  remains  a  cleft-like  space 
which  communicates  with  the  lumen  of  the  corresponding  urinifer- 
ous  tubule.  In  the  adult  the  glomerular  epithelium  is  very  flat, 
with  nuclei  projecting  slightly  into  the  open  space  of  the  Malpig- 
hian  corpuscle.  The  epithelium  of  the  outer  wall  is  somewhat 
higher,  but  still  of  the  squamous  type.  The  capsule  of  Bowman 
communicates  with  the  proximal  convoluted  tubule  by  means  of  a 
short  and  narrow  neck.  Its  epithelium  passes  over  gradually  into 


Fig.  246. — From  section  of  cortical  substance  of  human  kidney  ;  X  24°  :  a>  Epi- 
thelium of  Bowman's  capsule  ;  b  and  d,  membrana  propria  ;  c,  glomerular  epithelium  ; 
e,  blood-vessels  ;  /,  lobe  of  the  glomerulus;  g,  commencement  of  uriniferous  tubule; 
A,  epithelium  of  the  neck  ;  i,  epithelium  of  proximal  convoluted  tubule. 

the  cubical  epithelium  of  the  neck,  which,  in  turn,  merges  into  that 
of  the  proximal  convoluted  tubule. 

The  proximal  convoluted  portion,  from  40  fJ.  to  70  ft  in  diameter, 
is  lined  by  short  columnar  epithelial  cells,  the  protoplasm  of  which 
is  striated  and  may  be  separated  by  means  of  certain  reagents  into 
fibers  (R.  Heidenhain,  83).  In  man  the  nuclei  are  situated  in  the 
upper  portions  of  the  cells,  while  the  basal  portions  show  the  stria- 
tion  more  distinctly.  The  cells,  especially  in  their  indifferent,  non- 
striated  regions,  are  so  intimately  connected  that  the  cell  limits 
are  not  always  distinguishable.  In  well-fixed  preparations  the 
inner  portions  of  the  cells  often  show  a  narrow  striated  border, 


THE    URINARY    ORGANS. 


291 


often  giving  the  appearance  of  short  cilia.  In  the  guinea-pig 
the  basal  regions  of  the  lateral  surfaces  of  the  cells  constituting  the 
epithelium  of  the  proximal  convoluted  portion  present  numerous 
projections  which  interlock  and  give  to  a  surface  view  an  irregular 
fringe-like  outline.  In  cross-section  the  cells  appear  to  be  striated 
from  their  bases  upward  to  the  middle  of  the  nucleus.  Here,  how- 
ever, the  striation  is  without  doubt  due  to  the  outlines  of  the  irreg- 
ular ridges.  (Fig.  248.)  These  structural  relations  have  lately  been 
confirmed  in  the  case  of  the  guinea-pig,  and  also  found  to  hold 
true  for  man  (Landauer).  This  striation  is  much  coarser  than  that 


Nuclei  of  en- 
dothelial 
cells  of  blood 
capillaries. 


Fig.  247. — Section  of  proximal  convoluted  tubules  from  man  ; 


found  by  Heidenhain,  but  both  are,  under  certain  circumstances, 
seen  together. 

The  descending  limb  of  Henle's  loop,  from  Q/J,  to  1 5  //  in  diameter, 
is  narrow  and  possesses  flattened  epithelial  cells,  the  centers  of 
which,  containing  the  nuclei,  project  into  the  lumen  of  the  tubule. 
These  central  projections  of  the  cells  are  not  directly  opposite  those 
of  the  cells  on  the  opposite  wall,  but  alternate  with  the  latter,  thus 
giving  to  the  lumen  a  zigzag  outline  corresponding  to  the  length  of 
the  cell.  The  thick  portion  of  the  loop,  for  the  most  part  repre- 
sented by  the  ascending  limb,  from  23^  to  28 //  in  diameter,  possesses 
a  columnar  epithelium  similar  to  that  of  the  proximal  convoluted 


292 


THE    GENITOURINARY    ORGANS. 


portion.  Here,  however,  the  basal  striation  of  the  cells  is  not  so 
distinct,  the  lumen  is  somewhat  larger  than  that  of  the  descending 
limb,  and  by  treatment  with  certain  reagents  the  epithelium  may 


Nucleus. 


-  Nucleus. 


Fig.  248. — Epithelium  from  proximal  convoluted  tubule  of  guinea-pig,  with  surface 
and  lateral  views  (chrome- silver  method)  ;  X  59°  :  a>  at  The  irregular  interlacing  pro- 
jections. 


Fig.  249. — From  cortical  portion  of  longitudinal  section  of  kidney  of  young  child. 

often  be  separated  as  a  whole  from  the  underlying  basement  mem- 
brane. 

The  distal  convoluted  or  intercalated  portion,  from  39 p.  to  45//  in 


THE    URINARY    ORGANS. 


293 


diameter,  is  only  slightly  curved  (2  to  4  convolutions).  Its  epi- 
thelium is  relatively  high,  though  not  so  high  as  that  lining  the 
proximal  convoluted  portion  and  not  so  distinctly  striated.  The 
cells  are  provided  with  large  nuclei  and  their  basal  portions  are 
joined  by  interlacing  projections. 

The  next  important  segment  is  the  short  arched  collecting  portion, 
which  has  nearly  cubical  epithelial  cells  and  a  lumen  somewhat  wider 
than  that  of  the  intercalated  tubule.  The  smaller  straight  collecting 
tubules  have  a  low  columnar  epithelium  with  cells  of  somewhat  ir- 
regular shape,  the  frasal  portions  of  which  are  provided  with  short, 
irregular,  intertwining  processes,  which  serve  to  hold  the  cells  in 


-^  © 

Fig.   250. — Section  of  medulla  of  human  kidney;    X  about  300:  a,  a,  a.  Ascending 
limb  of  Henle's  loop  ;  l>,  by  b,  blood-vessels  ;  c,  ct  c,  descending  limb  of  Henle's  loop. 

place.  The  diameter  of  the  collecting  tubules  measures  from  45  ft 
to  75  /2. 

In  the  larger  collecting  tubules  the  epithelium  is  more  regular 
and  becomes  higher  as  the  tube  widens.  These  tubules  gradually 
unite  within  the  Malpighian  pyramid  and  the  regions  adjacent  to 
the  columns  of  Bertini  to  form  about  20  papillary  ducts  from  200^ 
to  300  fi  in  diameter.  The  latter  have  a  high  columnar  epithelium, 
and  empty  into  the  pelvis  of  the  kidney  at  the  apex  of  the  papilla, 
forming  the  foramina  papillaria. 

Besides  the  epithelium,  the  uriniferous  tubules   possess  an  ap- 


294 


THE    GENITO-URINARY    ORGANS. 


parently  structureless  membrana  propria,  that  of  the  collecting- 
tubules  being  very  thin.  According  to  Riihle  (97),  the  membrana 
propria  of  the  uriniferous  tubules  consists  of  fine  circular  and  longi- 
tudinal fibers  which  are  at  no  point  connected  with  the  cells,  and 
which  represent  nothing  more  than  a  thickened  and  more  regularly 
distributed  layer  of  the  interstitial  reticular  tissue.  The  basement 
membrane  of  the  vascular  loops  in  the  glomeruli  also  appears  to 
have  a  fibrous  structure  and  presents  numerous  fine  openings. 

Between  the  Malpighian  pyramids  are  found  the  columns  of 
Bertini,  presenting  a  structure  similar  to  that  of  the  cortex  of  the 
kidney,  and  extending  to  the  hilum  of  the  kidney. 

Between  the  uriniferous  tubules  and  surrounding  the  blood- 
vessels of  the  kidney  there  is  found  normally  a  small  amount  of 
connective  tissue.  Between  the  convoluted  portions  of  the  tubules 
this  is  present  only  in  small  quantity,  a  somewhat  greater  amount 


Papillary  duct. 
I 


Blood-vessel. 


Fig.  251. — From  longitudinal  section  through  papilla  of  injected  kidney;  X  4°  :  ai  Epi- 
thelium of  collecting  tubule  under  greater  magnification. 


being  found  in  the  neighborhood  of  the  Malpighian  corpuscles,  in 
the  boundary  zone  between  the  cortex  and  medulla  and  between 
the  larger  collecting  tubules  in  the  apices  of  the  Malpighian  pyra- 
mids. 

From  what  has  been  said  concerning  the  uriniferous  tubule  it 
must  be  evident  that  its  course  is  a  very  tortuous  one.  Beginning 
with  the  Malpighian  corpuscles,  situated  in  the  cortex  between  the 
medullary  rays,  the  tubule  winds  from  the  cortex  to  the  medulla 
and  back  again  into  the  cortex,  where  it  ends  in  a  collecting  tubule, 
which  passes  to  the  medulla  to  terminate  at  the  apex  of  a  Malpig- 
hian pyramid.  The  different  portions  of  the  tubules  have  the 
following  positions  in  the  kidney  :  In  the  cortex  between  the  medul- 
lary rays  are  found  the  Malpighian  corpuscles,  the  neck,  the  proxi- 
mal and  distal  convoluted  portions  of  the  uriniferous  tubule,  and  the 


THE    URINARY    ORGANS.  2Q5 

arched  collecting  tubules.  The  medullary  rays  are  formed  by  the 
cortical  portions  of  the  straight  collecting  tubules  and  a  portion  of 
the  ascending  limbs  of  Henle's  loops.  The  medulla  is  made  up 
mainly  of  straight  collecting  tubules  of  various  sizes  and  of  the  de- 
scending limbs  and  loops  of  Henle's  loops,  the  latter  being  often 
found  in  the  boundary  zone  between  the  cortex  and  medulla. 
(See  Fig.  250.) 

The  blood-vessels  of  the  kidney  have  a  characteristic  distribu- 
tion, and  are  in  the  closest  relationship  to  the  uriniferous  tubules. 


Boundary  line 
between  two 
Malpighian 
pyramids. 


*'•*"'--  Uriniferous 
tubules. 


-Glomerulus. 


Fig.  252. — Section  through  junction  of  two  lobules  of  kidney,  showing  their 
coalescence  ;  from  new-born  infant. 

The  renal  artery  divides  in  the  neighborhood  of  the  hilum  into  two 
branches, — a  dorsal  and  a  ventral, — which  again  divide,  the  result- 
ing trunks  giving  off  lateral  branches  to  the  renal  pelvis,  supplying 
its  mucous  membrane  and  then  breaking  up  into  capillaries  which 
extend  as  far  as  the  "  area  cribrosa."  The  venous  capillaries  of 
this  region  empty  into  veins  which  accompany  the  arteries.  Besides 
these,  other  arteries  originate  from  the  principal  branches,  or  from 
their  immediate  offshoots,  and  pass  backward  to  supply  the  walls 
of  the  renal  pelvis,  the  renal  capsule,  and  the  ureter.  The  main 


296  THE    GENITOURINARY    ORGANS. 

trunks  themselves  penetrate  at  the  hilum,  and  divide  in  the  columns 
of  Bertini  to  form  arterial  arches  (arteriae  arciformes)  which  extend 
between  the  cortical  and  medullary  substances.  Numerous  vessels, 
the  intralobular  arteries,  originate  from  the  arteriae  arciformes  and 
penetrate  into  the  cortical  pyramids  between  the  medullary  rays. 
Here  they  give  off  numerous  twigs,  each  of  which  ends  in  the 
glomerulus  of  a  Malpighian  corpuscle.  These  short  lateral  twigs 
are  the  vasa  afferentia.  Each  glomerulus  is  formed  by  the  breaking 
down  of  its  afferent  vessel,  which,  on  entering  the  Malpighian  cor- 
puscle, divides  into  a  number  of  branches,  each  in  turn  subdividing 
into  a  capillary  net.  From  each  of  these  nets  the  blood  passes 
into  a  somewhat  larger  vessel  constituting  one  of  the  branches  of 
the  efferent  vessel  which  carries  the  blood  away  from  the  glomerulus. 
Since  the  afferent  and  efferent  vessels  lie  in  close  proximity,  the 
capillary  nets  connecting  them  are  necessarily  bent  in  the  form  of 
loops.  The  groups  of  capillaries  in  a  glomerulus  are  separated  from 
each  other  by  a  larger  amount  of  connective  tissue  than  separates 
the  capillaries  themselves,  so  that  the  glomerulus  may  be  divided 
into  lobules.  In  shape  the  glomerulus  is  spheric,  and  is  covered 
by  a  thin  layer  of  connective  tissue  over  which  lies  the  inner  mem- 
brane of  the  capsule,  the  glomerular  epithelium.  On  its  exit  from 
the  glomerulus  the  vas  efferens  separates  into  a  new  system  of 
capillaries,  which  gradually  becomes  venous  in  character.  Thus,  the 
capillaries  which  form  the  glomerulus,  together  with  the  vas  efferens, 
are  arterial,  and  may  be  included  in  the  category  of  the  so-called 
arterial  retia  mirabilia.  Those  capillaries  formed  by  the  vas  efferens 
after  its  exit  from  the  Malpighian  corpuscle  lie  both  in  the  medullary 
rays  and  in  the  cortical  pyramids.  The  meshes  of  the  capillary  net- 
works distributed  throughout  the  medullary  rays  are  considerably 
longer  than  those  of  the  networks  supplying  the  cortical  pyramids 
and  labyrinth,  the  latter  being  quadrate  in  shape.  The  glomeruli 
nearest  the  renal  papillae  give  off  longer  vasa  efferentia  which  extend 
into  the  papillary  region  of  the  Malpighian  pyramids  (arteriolae 
rectae  spuriae)  and  form  there  capillaries  which  ramify  throughout 
the  papillae  with  oblong  meshes. 

Arterial  retia  mirabilia  also  occur  in  the  course  of  the  vasa 
afferentia  between  the  intralobular  arteries  and  the  glomeruli,  but 
nearer  the  latter.  Each  is  formed  by  the  breaking  down  of  the  small 
afferent  vessels  into  from  two  to  four  smaller  branches,  which  then 
reunite  to  pass  on  as  a  single  vessel.  In  structure  these  retia  differ 
greatly  from  the  glomeruli  in  that  here  the  resulting  twigs  are  not 
capillaries  and  have  nothing  to  do  with  the  secretion  of  urine 
(Golubew). 

From  the  vasa  afferentia  arterial  twigs  are  occasionally  given 
off,  which  break  down  into  capillaries  within  the  cortical  substance. 
Other  arteries  originate  from  the  lower  portion  of  the  intralob- 
ular arteries  or  from  the  arciform  arteries  themselves  and  enter 
the  medullary  substance,  where  they  form  capillaries.  These 


THE    URINARY    ORGANS. 


297 


vessels  constitute  the  so-called  "  arteriolae  rectae  verae."  Their 
capillary  system  is  in  direct  communication  with  the  capillaries 
of  the  vasa  afferentia  and  "vasa  recta  spuria."  The  mtralobular 
arteries  are  not  entirely  exhausted  in  supplying  the  vasa  afferentia 
which  pass  to  the  glomeruli.  A  few  extend  to  the  surface  of  the 
kidney  and  penetrate  into  the  renal  capsule,  where  they  termin- 
ate in  capillaries  which  communicate  with  those  of  the  recur- 
rent, suprarenal,  and  phrenic  arteries,  etc.  Smaller  branches 


Artery  of 
capsule. 


Arched  collecting 
tubule. 

Straight  collect- 
ing tubule. 

Distal  convoluted 
tubule. 


Malpighian     cor- 
puscle. 

Proximal    convo- 
luted tubule. 
Loop  of  Henle. 


Collecting  tubule. 


Arteria  arcuata. 


Capillary  net- 
work. Vas 
afferens. 


Glomerulus. 


Vena  arcuata. 


Large  collecting 
tubule. 


Papillary  duct. 


Fig.  253. — Diagrammatic  scheme  of  uriniferous  tubules  and  blood-vessels   of  kidney. 
Drawn  in  part  from  the  descriptions  of  Golubew. 


from  these  latter  vessels  may  penetrate  the  cortex  and  form 
glomeruli  of  their  own  in  the  renal  parenchyma  (arteriae  capsulares 
glomeruliferae).  These  relations,  first  described  by  Golubew,  are 
of  importance  not  only  in  the  establishment  of  a  collateral  circula- 
tion, but  also  as  a  partial  functional  substitute  in  case  of  injury  to 
the  renal  arteries.  The  same  author  also  confirms  the  statements 
of  Hoyer  (77)  and  Geberg,  that  between  the  arteries  and  veins  of 
the  kidney,  in  the  cortical  substance,  in  the  columns  of  Bertini,  and 


298 


THE    GENITOURINARY    ORGANS. 


—   A 


at  the  bases  of  the   Malpighian  pyramids,  etc.,  direct  anastomoses 
exist  by  means  of  precapillary  twigs. 

From  the  capillaries  the  venous  blood  is  gathered  into  small 
veins  which  pass  out  from  the  region  of  the  medullary  rays  and 
cortical  pyramids  and  unite  to  form  the  "intralobular  veins."  These 
have  an  arrangement  similar  to  that  of  the  corresponding  arteries. 
The  venous  blood  of  the  labyrinthian  capillaries  also  flows  into  the 
intralobular  veins,  and  as  a  result  a  peculiar  arrangement  of  these 
vessels  is  seen  at  the  surface  of  the  kidney  where  the  capillaries 
pass  radially  toward  the  terminal  branches  of  the  intralobular  veins 
and  form  the  stellate  figures  known  as  the  vena  stellatcz.  This  sys- 
tem is  also  connected  with  those  venous  capillaries  of  the  capsule 

which  do  not  empty  into  the  veins  ac- 
companying the  arteries  of  the  capsule. 
The  capillary  system  of  the  Malpighian 
pyramids  unites  to  form  veins,  the 
"venulae  rectae,"  which  empty  into  the 
venous  arches  (venae  arciformes)  which 
lie  parallel  with  and  adjacent  to  the 
corresponding  arteries.  The  larger 
veins  are  found  side  by  side  with  the 
arteries  and  pass  out  at  the  hilum  of  the 
organ. 

The  lymph-vessels  of  the  kidneys 
need  to  be  investigated  further.  Lymph 
clefts  have  been  observed  in  the  cortex 
between  the  convoluted  tubules  ;  these 
have  been  traced  into  larger  vessels 
found  in  the  capsule. 

The  kidneys  receive  their  innerva- 
tion  through  nonmedullated  and  medul- 
lated  nerve-fibers.  The  former  accom- 
pany the  arteries  and  may  be  traced 
along  these  to  the  Malpighian  corpus- 
cles. From  the  plexuses  surrounding  the  vessels  small  branches  are 
given  off,  which  end  on  the  muscle-cells  of  the  media.  According  to 
Berkley,  small  nerve-fibrils  may  be  traced  to  the  uriniferous  tubules, 
which  pierce  the  membrana  propria  and  end  on  the  epithelial  cells. 
Dogiel  has  shown  that  medullated  (sensory)  nerve-fibers  terminate 
in  the  adventitia  of  the  arteries  of  the  capsule. 

The  most  important  investigations  into  the  secretory  processes 
of  the  uriniferous  tubules  are  those  of  R.  Heidenhain  (83)  who 
used  indigo-carmin  in  his  researches.  If  a  saturated  aqueous 
solution  of  indigo-carmin  be  injected  into  the  blood-vessels  of  a 
rabbit,  the  elimination  of  the  substance  will  be  found  to  take  place 
through  the  kidneys  as  well  as  by  means  of  the  other  excretions. 
Microscopic  examination  of  such  a  kidney  reveals  the  fact  that  the 
proximal  convoluted  tubules  and  ascending  limbs  of  the  loops  of 


Fig.  254. — A,  Direct  anasto- 
mosis between  an  artery  and  vein 
in  a  column  of  Berlin  of  child  ; 
£,  bipolar  rete  mirabile  inserted 
in  the  course  of  an  arterial  twig. 
Dog's  kidney  (after  Golubew). 


THE   URINARY    ORGANS.  299 

Henle  are  alone  concerned  in  the  elimination  of  the  substance, 
while  apparently  water  alone  is  filtered  through  the  remaining  seg- 
ments of  the  uriniferous  tubules.  Among  others,  Disse  has 
recently  taken  up  the  subject  of  cellular  secretion  in  the  uriniferous 
tubules.  According  to  him,  we  may  distinguish  in  the  convoluted 
tubules  (i)  those  with  a  wide  lumen,  having  low  cells  apparently 
with  no  cell  limits  and  no  distinct  basilar  zone,  but  with  peculiar 
structures  which  may  be  likened  to  cuticulae,  so  called,  or  a  striated 
border  (Tornier)  (Fig.  247) ;  (2)  tubules  with  a  narrow  lumen  and 
wedge-shaped  epithelial  cells,  with  indistinct  cell  limits  and  diffusely 
granular  protoplasm  ;  (3)  tubules  with  an  extremely  narrow  lumen 
and  high  epithelial  cells  with  differentiated  protoplasm,  the  basal 
portion  of  which  is  dark  and  striated,  the  upper  clear  and  contain- 
ing the  nucleus.  These  results  are  not,  however,  confirmed  by  the 
painstaking  researches  of  Sauer.  This  author  finds  that  the  secre- 
tory portions  of  the  uriniferous  tubules  (convoluted  portions  of  the 
tubules  and  part  of  the  loops  of  Henle)  always  have  the  same  un- 
changed epithelium,  but  that,  during  secretion,  the  lumina  of  the 
tubules  are  subject  to  great  variation  ;  in  tubules  with  scarcely 
recognizable  lumina  the  epithelial  elements  are  high  and  narrow  ;  in 
those  with  wide  lumina,  low  and  broad.  In  the  former  the  stria- 
tion  of  Heidenhain  is  naturally  fine  ;  in  the  latter,  somewhat  coarser. 
The  peculiar  terminations  of  Tornier  are  found  by  Sauer  during  all 
phases  of  secretion.  According  to  this  view,  then,  neither  the 
striation  of  Heidenhain  nor  the  terminations  of  Tornier  are  tem- 
porary appearances  due  to  a  particular  phase  of  secretion,  but 
represent  permanent  structural  peculiarities  of  the  cells  in  certain 
definite  portions  of  the  uriniferous  tubules.  The  volumetric 
changes  in  the  uriniferous  tubules  also  probably  influence  the  form 
and  number  of  the  indentations  in  the  epithelial  cells  described  on 
page  291, 

The  permanent  kidney  is  developed  as  early  as  the  fifth  week  of 
embryonic  life.  The  renal  anlagen,  from  which  the  epithelium  of 
the  ureter,  renal  pelvis,  and  uriniferous  tubules  is  formed,  originate 
from  the  median  portion  of  the  posterior  wall  of  the  Wolffian  duct. 
These  buds  grow  with  their  blind  ends  extending  anteriorly,  and  are 
soon  surrounded  by  cellular  areas,  the  blastema  of  the  kidneys. 
After  the  renal  bud  has  become  differentiated  into  a  narrow  tube 
(the  ureter)  and  a  wider  central  cavity  (the  renal  pelvis)  hollow 
epithelial  buds  are  developed  from  the  latter.  These  extend  radi- 
ally toward  the  surface  of  the  renal  anlagen,  where  they  undergo  a 
T-shaped  division.  These  latter  are  the  first  traces  of  the  papillary 
ducts  and  collecting  tubules.  The  cup-shaped  capsules  are  formed 
by  the  invagination  of  the  ends  of  the  tubules  by  the  glomeruli 
which  originate  separately  and  in  this  way  become  connected  with 
the  uriniferous  tubules.  The  remaining  portions  of  the  adult  urin- 
iferous tubules  are  gradually  formed  from  the  tubes  connecting  the 
glomeruli  with  the  collecting  tubules. 


300 


THE    GENITO-URINARY    ORGANS. 


2.  THE  PELVIS  OF  THE  KIDNEY,  URETER,  AND  BLADDER. 

The  renal  pelvis,  ureter,  and  urinary  bladder  are  lined  by  strati- 
fied transitional  epithelium.  Its  basal  cells  are  nearly  cubical ; 
these  support  from  two  to  five  rows  of  cells  of  varying  shape.  They 
may  be  spindle-shaped,  irregularly  polygonal,  conical,  or  sharply 
angular,  and  provided  with  processes.  Their  variation  in  form  is 
probably  due  to  mutual  pressure.  The  superficial  cells  are  large 


Superficial   epi- 
thelial cells. 


Mucosa. 


Epithelium. 


Mucosa. 


Inner  longitud- 
inal muscular 
layer. 


Middle  circular 
muscular 
layer. 


Outer  muscular 
layer. 


Fig-  255. — Section  of  lower  part  of  human  ureter  ;  X  I4°- 

and  cylindric,  a  condition  characteristic  of  the  ureter  and  bladder. 
Their  free  ends  and  lateral  surfaces  are  smooth,  but  their  bases  pre- 
sent indentations  and  projections  due  to  the  irregular  outlines  of  the 
underlying  cells.  The  superficial  cells  often  possess  two  or  more 
nuclei. 

The  mucosa  often  contains  diffuse  lymphoid  tissue,  which  is  more 
highly    developed    in    the    region    of   the    renal    pelvis.       A   few 


THE    SUPRARENAL    GLANDS.  3<DI 

mucous  glands  are  also  met  with  in  the  pelvis  and  in  the  upper  por- 
tion of  the  ureter.  The  ureter  possesses  two  layers  of  nonstriated 
muscle-fibers — the  inner  longitudinal,  the  outer  circular.  From  the 
middle  of  the  ureter  downward  a  third  external  muscular  layer  is 
found  with  nearly  longitudinal  fibers. 

The  urinary  bladder  has  no  glands,  and  its  musculature  appar- 
ently consists  of  a  feltwork  of  nonstriated  muscle  bundles,  a  condi- 
tion particularly  well  seen  in  sections  of  the  dilated  organ.  But  even 
here  three  indistinct  muscle  layers  may  be  distinguished,  the  outer 
and  inner  layers  being  longitudinal  and  the  middle  circular.  A 
remarkable  peculiarity  of  these  structures  is  the  extreme  elasticity 
of  their  epithelium,  the  cells  flattening  or  retaining  their  natural 
shape  according  to  the  amount  of  fluid  in  the  cavities  which  they 
line  (compare  London,  Kann). 

The  nerve  supply  of  the  bladder  has  been  studied  by  Retzius, 
Huber,  and  Griinstein  in  the  frog  and  a  number  of  the  smaller 
mammalia.  Numerous  sympathetic  ganglia  are  observed,  situated 
outside  of  the  muscular  coat,  at  the  base  and  sides  of  the  bladder. 
The  neuraxes  of  the  sympathetic  neurones  of  these  ganglia  are 
grouped  into  smaller  or  larger  bundles  which  interlace  and  form 
plexuses  surrounding  the  bundles  of  nonstriated  muscle-cells.  From 
these  plexuses  nerve-fibers  are  given  off,  which  penetrate  the  muscle 
bundles  and  end  on  the  muscle-cells.  The  cell-bodies  of  the  sym- 
pathetic neurones  are  surrounded  by  the  telodendria  of  small 
medullated  fibers,  which  terminate  in  the  ganglia.  Passing  through 
the  ganglia  large  medullated  fibers  (sensory  nerves)  may  be  ob- 
served which  pass  through  the  muscular  coat,  branch  repeatedly 
in  the  mucosa,  and  lose  their  medullary  sheaths  on  approaching 
the  epithelium  in  which  they  end  in  numerous  telodendria,  the 
small  branches  of  which  terminate  between  the  epithelial  cells. 

The  ureters  are  surrounded  by  a  nerve  plexus  containing  non- 
medullated  and  medullated  nerve-fibers.  The  former  end  on  cells 
of  the  muscular  layers  ;  the  latter  pass  through  the  muscular  layer, 
and  on  reaching  the  mucosa  branch  a  number  of  times  before  losing 
thefr  medullary  sheaths.  The  nonmedullated  terminal  branches 
form  telodendria,  the  terminal  fibers  of  which  have  been  traced 
between  the  cells  of  the  lining  epithelium  (Huber). 


B*  THE  SUPRARENAL  GLANDS. 

The  suprarenal  gland  is  surrounded  by  a  fibrous-tissue  capsule 
containing  nonstriated  muscle-cells,  blood-  and  lymph-vessels, 
nerves,  and  sympathetic  ganglia.  The  glandular  structure  is  divided 
into  a  cortical  and  a  medullary  portion.  In  the  former  are  distin- 
guished three  layers,  according  to  the  arrangement,  shape,  and 
structure  of  its  cells — an  outer  glomerular  zone,  a  middle  broad  fas- 
cicular  zone,  and  an  inner  reticular  zone.  According  to  Flint,  who 


302 


THE    GENITOURINARY    ORGANS. 


worked  in  Mall's  laboratory,  and  whose  account  will  here  be  fol- 
lowed, the  framework  of  the  gland  is  made  up  of  reticulum.  In 
the  glomerular  zone  this  reticulum  is  arranged  in  the  form  of  septa, 
derived  from  the  capsule,  which  divide  this  zone  into  more  or  less 
regular  spaces  of  oval  or  oblong  shape.  In  the  fascicular  zone  the 
reticulum  is  arranged  in  processes  and  fibrils  running  at  right 
angles  to  the  capsule.  In  the  reticular  zone  the  fibrils  form  a  dense 
network,  while  in  the  medulla  the  reticular  fibrils  are  arranged  in 
processes  and  septa  which  outline  numerous  spaces. 


Capsule. 


Zona  glomerulosa. 


>.    Zona  fasciculata. 


Zona  reticularis. 


Fig.  256. — Section  of  suprarenal  cortex  of  dog  ;   X  I2°- 

The  gland-cells  of  the  glomerular  zone  are  arranged  in  coiled  col- 
umns of  cells  found  in  the  compartments  formed  by  the  septa  of 
reticulum  above  mentioned.  The  cells  composing  these  columns 
are  irregularly  columnar,  with  granular  protoplasm  and  deeply  stain- 
ing nuclei.  In  the  fascicular  zone  the  cells  are  arranged  in  regular 
columns,  consisting  usually  of  two  rows  of  cells,  and  situated  be- 
tween the  reticular  processes,  which  run  at  right  angles  to  the  cap- 


THE    SUPRARENAL    GLANDS.  303 

sule.  The  cells  of  this  zone  are  polyhedral  in  shape,  with  gran- 
ular protoplasm  often  containing  fat  droplets  and  with  nuclei 
containing  little  chromatin.  Similar  cells  are  found  in  the  reticular 
zone,  but  here  they  are  found  in  small  groups  situated  in  the  meshes 
of  the  reticulum.  The  cells  of  the  medullary  substance  are  less 
granular  and  smaller  in  size  than  those  of  the  cortex,  and  are 
grouped  in  irregular,  round,  or  oval  masses  bounded  by  the  septa  of 
reticulum.  These  cells  stain  a  deep  brown  with  chromic  acid  and  its 


Fig.  257. — Arrangement  of  the  intrinsic  blood-vessels  in  the  cortex  and  medulla  of 
the  dog's  adrenal  (Fig.  17,  Plate  V,  of  Flint's  article  in  "  Contributions  to  the  Science 
of  Medicine,"  dedicated  to  Professor  Welch,  1900). 

salts,  and  the  color  can  not  be  washed  out  with  water — a  peculiarity 
which  shows  itself  even  during  the  development  of  these  elements, 
and  which  is  possessed  by  few  other  types  of  cells.  Numerous 
ganglion  cells,  isolated  and  in  groups,  and  many  nerve-fibers  occur 
in  this  portion  of  the  organ. 

The  blood-vessels  of  the  suprarenal  glands  are  of  special  interest, 
since  it  has  been  shown  that  the  secretion  of  the  glands  passes 
directly  or  indirectly  into  the  vessels.  The  following  statements 


304  THE  GENITOURINARY  ORGANS. 

we  take  from  Flint  :  The  blood-vessels,  derived  from  various 
sources,  form  in  the  dog  a  poorly  developed  plexus,  situated  in  the 
capsule.  From  this  plexus  three  sets  of  vessels  are  derived,  which 
are  distributed  respectively  in  the  capsule,  the  cortex,  and  the 
medulla  of  the  gland.  The  vessels  of  the  capsule  divide  into 
capillaries,  which  empty  into  a  venous  plexus  situated  in  the 
deeper  portion  of  the  capsule.  The  cortical  arteries  divide  into 
capillaries  which  form  networks,  the  meshes  of  which  correspond 
to  the  arrangement  of  the  cells  in  the  different  parts  of  the  cortex, 
encircling  the  coiled  columns  of  cells  in  the  glomerular  zone, 
while  in  the  fascicular  zone  the  capillaries  are  parallel  with  occa- 
sional anastomoses.  These  capillaries  form  a  fine-meshed  plexus 
in  the  reticular  zone  and  unite  in  the  peripheral  portion  of  the 
medulla  to  form  small  anastomosing  veins,  from  which  the  larger 
veins  are  derived.  The  latter  do  not  anastomose,  and  are  therefore 
terminal  veins.  The  arteries  of  the  medulla  pass  through  the 
cortex  without  giving  off  any  branches  until  the  medulla  is  reached, 
where  they  break  up  into  a  capillary  network  surrounding  the  cell 
masses  situated  here.  The  blood  from  this  plexus  may  be  col- 
lected into  veins  of  the  medulla  which  empty  into  the  terminal 
vein  or  some  of  its  larger  branches,  or  may  flow  directly  into 
branches  of  the  venous  tree.  The  endothelial  walls  of  the  capil- 
laries rest  directly  on  the  specific  gland  cells,  with  the  intervention 
here  and  there  of  a  few  reticular  fibrils.  According  to  Pfaundler, 
the  walls  of  the  blood-vessels  of  the  entire  suprarenal  body  consist 
solely  of  the  tunica  intima. 

The  nerves  of  the  suprarenal  glands  have  been  studied  recently 
by  Fusari  and  Dogiel  (94)  ;  the  description  given  by  the  latter  will 
here  be  followed.  Numerous  nerve-fibers,  both  nonmedullated  and 
medullated,  arranged  in  the  form  of  a  plexus  containing  sym- 
pathetic ganglia,  are  found  in  the  capsule.  From  this  plexus 
numerous  small  bundles  and  varicose  fibers  enter  the  cortex,  where 
they  form  plexuses  surrounding  the  columns  of  cells  or  groups  of 
cells  found  in  the  three  zones  of  the  cortex  and  about- the  vessels 
and  capillaries  of  the  cortex.  The  nerve-fibers  of  these  plexuses  are 
on  the  outside  of  the  columns  and  cell  groups  and  do  not  give 
off  branches  which  pass  between  the  cells.  The  nerve  supply  of 
the  medullary  substance  is  very  rich,  and  is  derived  mainly  from 
large  nerve  bundles  which  pass  from  the  plexus  in  the  capsule  to 
the  medulla,  where  they  divide  and  form  dense  plexuses  which 
surround  the  groups  of  gland-cells  and  veins  ;  from  these  plexuses 
fine  varicose  fibers  pass  between  the  gland-cells,  forming  intercel- 
lular plexuses.  In  the  medulla  there  are  found  in  many  animals 
large  numbers  of  sympathetic  cells,  some  isolated,  others  grouped 
to  form  small  ganglia.  Pericellular  networks  surround  the  cell- 
bodies  of  certain  of  these  sympathetic  cells.  (For  further  informa- 
tion concerning  the  suprarenal  glands  consult  Gottschau,  Weldon, 
Hans  Rabl,  C.  K.  Hoffmann  (92),  Pfaundler,  Flint,  and  Dogiel.) 


TECHNIC.  305 

TECHNIC. 

270.  The  arrangement  of  the  cortical  and  medullary  portions  of  the 
kidney  is  best  seen  in  sections  of  the  kidney  of  small  mammalia,  cut  in  the 
proper  direction,  and,  if  possible,  embracing  the  whole  organ.     If,  on  the 
other  hand,  the  finer  epithelial  structures  are  to  be  examined,  small  pieces 
are  first  fixed  in  osmic  acid  mixtures  or  in  corrosive  sublimate. 

271.  Impregnation  with   silver   nitrate  (method  of  Golgi  or  Cox) 
reveals  some  points  as  to  the  relation  of  the  cells  of  the  uriniferous  tubules 
to  each  other. 

272.  In  order  to  isolate  the  tubules,  thin  strips  of  kidney  tissue  are 
treated  for   from   fifteen   to   twenty  hours  with  pure   hydrochloric  acid 
having  a  specific  gravity  of  1.12  (for  this  purpose  kidney  tissue  is  used 
taken  from  an  animal  killed  twenty-four  hours  previously).     It  is  then 
washed,  teased,  and  examined  in  glycerin  (Schweiger-Seidel).     Fuming 
nitric  acid  (40%),  applied  for  a  few  hours  to  small  pieces  of  tissue,  occa- 
sionally isolates  the  uriniferous  tubules  very  extensively.     The  further 
treatment  is  then  the  same  as  after  hydrochloric  acid.     A  35%  potassium 
hydrate  solution  may  also  be  employed.     The  isolated  pieces  are,  however, 
not  easily  preserved  permanently. 

273.  The  epithelium  of  the  uriniferous  tubules  may  be  isolated  either 
in  y$  alcohol  (vid.  T.    128)  or,  according  to  R.   Heidenhain  (83),  in 
a   5%   aqueous   solution  of  neutral   ammonium  chromate.      The   latter 
method  shows  clearly  the  striation  of  the  epithelium. 

274.  The    autophysiologic    injection    with    indigo-carmin    (Chrzon- 
szczewsky  vid.  T.  245),  applied  as  in  the  case  of  the  liver,  fills  the  urin- 
iferous tubules,  which  may  then  be  further  examined  in  sections. 

275.  The  blood-vessels  are  examined  in  injected  specimens  (injection 
of  the  kidney  is  easily  accomplished).      In  larger  animals  the  injection  is 
made  into  the  renal  artery,  while  in  smaller  ones  the  whole  posterior  half 
of  the  body  is  injected  through  the  abdominal  aorta. 

276.  The  ureter  and  bladder  are  cut  open,  fixed,  and  then  sectioned. 
In  this  way  the  organs  are  shown  in  a  collapsed  condition,  in  which  the 
arrangement  of  the  epithelium  is  totally  different  from  that  found  in  the 
distended  organs.    In  order  to  observe  them  in  the  latter  condition  the  fix- 
ing agent  is  injected  into  the  ureter  or  bladder,  when,  after  proper  liga- 
tion,  they  are  placed  in  the  same  fixing  agent. 

277.  The  usual  fixing  fluids  are  employed  in  the  demonstration  of  the 
suprarenal  capsule  ;  but  mixtures  containing  chromic  acid,  whether  Flem- 
ming's  fluid,  chromic  acid,  or  its  salts,  are  of  special  importance  in  the 
examination  of  the  organ,  since  the  medullary  substance  of  the  suprarenal 
capsule  stains  a  specific  brown  when  treated  by  these  mixtures  (a  con- 
dition only  reduplicated  in  certain  cells  of  the  hypophysis).     This  brown 
staining  also  occurs  when  the  cortical  and  medullary  portions  are  entirely 
separated,  as  is  the  case  in  certain  animals  and  during  the  development 
of  the  suprarenal  capsule.     The  fat  found  in  the  cells  of  the  suprarenal 
cortex  is  not  identical  with  that  of  the  rest  of  the  body,  as  it  may  be  dis- 
solved by  chloroform  and  oil  of  bergamot  out  of  tissue  fixed  with  osmic 
acid  (Hans  Rabl). 

20 


306  THE    GENITOURINARY    ORGANS. 

C  THE  FEMALE  GENITAL  ORGANS* 

J.  THE  OVUM. 

The  product  of  the  ovaries  is  the  matured  "  ovum,"  or  egg,  hav- 
ing a  diameter  of  from  0.22  to  0.32  mm.  It  forms  a  single  cell 
with  a  thick  membrane,  from  7  p.  to  n  jut  in  thickness,  known  as 
the  zona  pellucida.  The  ovum  consists  of  a  cell-body  known  as 
the  yolk- or  vitellus,  and  a  nucleus,  from  30  p  to  40  p.  in  diameter, 
termed  the  germinal  vesicle.  The  vitellus  consists  of  two  sub- 
stances— a  protoplasmic  network,  with  a  somewhat  denser  arrange- 
ment at  the  periphery  of  the  cell  and  in  the  neighborhood  of  the 
germinal  vesicle,  and  of  small,  highly  refractive,  and  mostly  oval 
bodies  imbedded  between  the  meshes  of  the  protoplasm — the  yolk 
globules.  These  latter,  as  a  rule,  are  merely  browned  on  being 
treated  with  osmic  acid,  although  occasionally  a  true  fatty  reaction 
may  be  obtained.  The  germinal  vesicle  is  surrounded  by  a  distinct 
membrane  having  a  double  contour.  In  its  interior  we  find  a 
scanty  lining  framework  containing  very  little  chromatin,  and  one  or 
two  relatively  large  false  nucleoli,  or  germinal  spots,  from  ///  to  io// 
in  diameter,  due  to  a  nodal  thickening  of  the  chromatin.  In  the 
latter  a  further  very  distinct  differentiation  is  sometimes  seen  in  the 
shape  of  a  small  body  (vacuole?)  of  doubtful  origin,  which  has 
been  called  Schron's  granule.  The  germinal  vesicle  and  spot  were 
formerly  known  as  "  Purkinje's  vesicle"  and  "  Wagner's  spot," 
respectively,  from  their  discoverers. 

2.  THE  OVARY. 

The  ovaries  are  almost  entirely  covered  by  peritoneum.  The 
mesothelial  cells  of  the  latter,  however,  undergo  here  a  differentia- 
tion, to  form  the  germinal  epithelium.  At  the  hilum  the  peritoneal 
covering  is  absent,  and  it  is  here  that  the  connective-tissue  elements 
of  the  ovarian  ligament  penetrate  into  the  organ  to  form  its  con- 
nective-tissue framework,  the  so-called  stroma  of  the  ovary.  At  an 
early  period  in  the  development  of  the  ovaries,  the  germinal  epithe- 
lium begins  a  process  of  imagination  into  the  stroma  of  the  ovary, 
so  that  at  the  periphery  of  the  organ  a  zone  is  soon  formed  which 
consists  of  both  connective  tissue  and  epithelial  (mesothelial)  ele- 
ments. This  zone  is  called  the  cortex,  or  parenchymatous  zone. 
That  portion  of  the  organ  in  the  neighborhood  of  the  hilum  (aside 
from  the  rudimentary  structure  known  as  the  epoophoron)  consists 
of  connective  tissue  containing  numerous  elastic  fibers  and  unstriped 
muscle-cells,  and  is  known  as  the  medullary  substance,  or  vascular 
zone.  This  connective  tissue  penetrates  here  and  there  into  the  cor- 
tex, separates  the  epithelial  elements  of  the  latter  from  each  other, 
and  is  in  direct  continuation  with  a  stratum  immediately  beneath  the 
germinal  epithelium,  called  the  tunica  albuginea.  This  latter  layer 
of  connective  tissue  is  very  distinct  in  the  adult  ovary,  although  its 


THE    FEMALE    GENITAL    ORGANS. 


307 


structure  and  thickness  vary  to  a  considerable  extent.  In  young 
ovaries  it  is  irregular,  but  shows  in  its  highest  development  three 
layers  distinguishable  from  each  other  by  the  different  direction  of 
the  fibers.  In  the  medullary  substance  the  connective-tissue  fibers 
are  long,  in  the  cortex  short,  and  in  the  zone  containing  the  follicles 
(see  below)  are  mingled  with  numerous  connective -tissue  cells. 
Nonstriated  muscle-fibers  occur  exclusively  in  the  medulla.  Here 
they  are  gathered  in  bundles  which  accompany  the  blood-vessels, 
and  may  even  form  sheaths  around  the  latter.  They  are  especially 
prominent  in  mammalia. 

The  germinal  epithelium  is   distinguished   from  that  of  the  re- 
maining peritoneum  by  the  greater  height  of  its  cells,  which  are 

Young  follicle  with  ovum. 


Primordial  ova «& 


Ovum  with  fol- 
licular  epithe- 
lium. 


Fig.  258. — Section  from  ovary  of  adult  dog.  At  the  right  the  stellate  figure  repre- 
sents a  collapsed  follicle  with  its  contents.  Below  and  at  the  right  are  seen  the  tubules 
of  the  parovarium  (copied  from  Waldeyer). 

cubic  or  even  cylindric  in  shape.  At  an  early  period  in  the  devel- 
opment of  the  ovaries  this  epithelium  pushes  into  the  underlying 
embryonic  connective  tissue  in  solid  projections,  to  form  the  primary 
egg  tubes  of  Pfluger,  the  cells  of  which  very  soon  begin  to  show 
differentiation.  Some  retain  their  original  characteristics  and  shape, 
while  others  increase  in  size,  become  rounded,  and  develop  into  the 
young  ova.  Those  retaining  their  indifferent  type  become  the  fol- 
licular  cells  surrounding  the  egg.  This  differentiation  into  ova  and 
follicular  elements  may  even  occur  in  the  germinal  epithelium  itself, 
in  which  case  the  larger  round  cells  are  known  as  the  primitive  or 
primordial  ova.  In  the  further  development  of  the  ovarian  cortex 


308 


THE    GENITOURINARY    ORGANS. 


the  primitive  egg  tubes  are  penetrated  throughout  by  connective 
tissue,  so  that  each  egg  tube  is  separated  into  a  number  of  irregular 
divisions.  In  this  way  a  number  of  distinct  epithelial  nests  are 
formed,  which  lose  their  continuity  with  the  germinal  epithelium 
and  finally  lie  imbedded  in  the  connective  tissue.  According  to  the 
shape  and  other  characteristics  of  these  epithelial  nests,  we  may 
distinguish  several  different  groups:  (i)  The  primitive  egg  tubes 


fcMifz*   O&ttV>S&j£a#.f4I 


Germinal  epi- 

—  thelium. 
••<>  Tunica    albu- 

ginea. 

—  Follicular 
^^      epithelium. 

~~  Ovum. 


Granular  layer  of 
large  Graafian 
follicle. 


Fig.  259. — From  ovary  of  young  girl ;   X  I9°- 


of  Pfliiger ;  (2)  the  typical  primitive  follicles — i.  e.t  those  which 
contain  only  a  single  egg-cell  (present  in  the  twenty -eighth  week  of 
fetal  life)  ;  (3)  the  atypic  follicles — i.  e.,  those  containing  from  two 
to  three  egg-cells  ;  (4)  the  so-called  nests  of  follicles,  in  which  a 
large  number  of  follicles  possess  only  a  single  connective-tissue  en- 
velope ;  (5)  follicles  of  the  last-named  type  which  may  assume  the 
form  of  an  elongated  tube,  and  which  are  then  known  as  the  con- 


THE  FEMALE  GENITAL  ORGANS.  309 

stricted  tubes  of  Pfliiger.  The  fourth,  fifth,  and  possibly  the  third 
types  are  further  divided  by  connective-tissue  septa,  until  they 
finally  form  distinct  and  typical  follicles  (Schottlander,  91,  93). 

In  the  adult  ovary  true  egg  tubes  are  no  longer  developed. 
Isolated  invaginations  of  the  germinal  epithelium  sometimes  occur, 
but  apparently  lead  merely  to  the  formation  of  epithelial  cysts 
(Schottlander).  The  theories  as  to  when  the  formation  of  new 
epithelial  nests  or  follicles  ceases  are,  however,  very  conflicting, 
some  authors  believing  that  cessation  takes  place  at  birth,  others 
that  it  continues  into  childhood  and  even  into  middle  age. 

The  typical  primitive  follicle  consists  of  a  relatively  large  egg- 
cell  surrounded  by  a  single  layer  of  smaller  cubical  or  cylindric 
follicular  cells.  The  growth  of  the  follicle  takes  place  by  means 
of  mitotic  division  in  the  follicular  cells  and  increase  in  size  of 
the  ovum.  The  egg-cell  is  soon  surrounded  by  several  layers  of 
cells,  and  gradually  assumes  an  eccentric  position  in  the  cell 
complex.  At  a  certain  distance  from  the  ovum  and  nearly  in  the 
center  of  the  follicle  one  or  more  cavities  form  in  the  follicular 
epithelium.  These  become  confluent,  and  the  resulting  space  is 
filled  by  a  fluid  derived,  on  the  one  hand,  from  a  process  of 
secretion  and,  on  the  other  hand,  from  the  destruction  of  some 
of  the  follicular  cells.  The  cavity  is  called  the  antrum  of  the 
follicle,  and  such  a  follicle  has  received  the  name  of  Graafian 
follicle.  Its  diameter  varies  from  0.5  to  6  mm.  The  follicle  in- 
creases in  size  through  cell-proliferation,  the  cavity  increasing  and 
gradually  inclosing  the  egg  together  with  the  follicular  cells  imme- 
diately surrounding  it,  although  the  latter  always  remain  connected 
with  the  wall  of  the  vesicle  at  some  point.  The  egg  now  lies 
imbedded  in  a  cell-mass,  the  discus  proligems,  which  is  composed 
of  follicular  epithelium,  and  projects  into  the  follicular  cavity. 
The  follicular  epithelium  forming  the  wall  of  the  cavity  is  known  as 
the  stratum  granuloswn,  the  cavity  as  the  antrum,  and  the  fluid 
which  it  contains  as  the  liquor  folliculi.  Those  follicular  cells 
which  immediately  surround  and  rest  upon  the  ovum  are  some- 
what higher  than  the  rest  and  constitute  the  egg  epithelium,  or 
corona  radiata. 

During  the  growth  of  the  follicle  the  connective  tissue  surround- 
ing it  becomes  differentiated  into  a  special  envelope,  called  the  thcca 
folliculi.  In  it  two  layers  may  be  distinguished — the  outer,  the 
tunica  externa,  consisting  of  fibrous  connective  tissue,  is  continu- 
ous with  the  inner,  or  tunica  interna,  rich  in  blood-vessels  and 
cellular  elements.  The  follicle  gradually  extends  to  the  surface  of 
the  ovary,  at  which  point  it  finally  bursts  (see  below),  allowing  the 
ovum  to  escape  into  the  body  cavity  and  thus  into  the  oviduct. 

During  the  growth  and  development  of  the  ovarian  follicles  the 
ova  undergo  certain  changes  of  size  and  structure  which  may  receive 
further  consideration.  These  have  been  described  for  the  human 
ovary  by  Nagel  (96),  whose  account  will  here  be  followed.  The 


Fig.  263. 

Figs.  260,  261,  262,  and  263.  — From  sections  of  cat's  ovary,  showing  ova  and 
follicles  in  different  stages  of  development ;  X  225  :  ai  a>  a>  a>  Germinal  spots  ;  b,  b,  b,  b, 
germinal  vesicles  ;  c,  c,  c,  c,  ova  ;  d,  d,  d,  zonse  pellucidae  ;  e,  <?,  e,  e,  corona  radiata  ; 
f,  ft  ft  ft  thecse  folliculorum  ;  g,  beginning  of  formation  of  the  cavity  of  the  follicle 
(compare  Fig.  266). 

310 


THE  FEMALE  GENITAL  ORGANS.  3  I  I 

ova  of  the  primitive  or  primordial  follicles  attain  a  size  (in  fresh  tissue 
teased  in  normal  salt  solution)  varying  from  48^  to  69^.  They 
possess  a  nucleus  varying  in  size  from  20  p.  to  32//,  presenting  a 
doubly  contoured  nuclear  membrane,  and  containing  a  distinct 
chromatin  network  with  a  nucleolus  and  several  accessory  nucleoli. 
The  protoplasm  shows  a  distinct  spongioplastic  network  containing 
a  clear  hyaloplasm.  The  primitive  ova,  until  they  undergo  further 
development,  retain  this  size  and  structure,  irrespective  of  the  age 
of  the  individual.  They  are  numerous  in  embryonic  life  and  early 
childhood,  always  found  during  the  ovulation  period,  but  not 
observed  in  the  ovaries  of  the  aged.  Changes  in  the  size  and 
structure  of  the  ova  accompany  the  proliferation  of  the  follicular 
cells  in  the  growing  follicles.  As  soon  as  the  follicular  cells  of  a 
primitive  follicle  proliferate,  as  above  described,  the  ovum  of  the 
follicle  increases  in  size  until  it  has  attained  the  size  of  a  fully 
developed  ovum.  The  zona  pellucida  now  makes  its  appearance, 
and  after  this  has  reached  a  certain  thickness,  yolk  granules  (deuto- 
plastic  granules)  develop  in  the  protoplasm  of  the  ovum.  In  a 
fully  developed  Graafian  follicle  the  ovum  presents  an  outer  clearer 
protoplasmic  zone  and  an  inner  fine  granular  zone  containing  yolk 
granules  ;  in  the  former  lies  the  germinal  vesicle.  Between  the 
protoplasm  of  the  ovum  and  the  zona  pellucida  is  found  a  narrow 
space  known  as  the  perivitelline  space.  The  germinal  vesicle 
(nucleus),  which  is  usually  of  spheric  shape,  possesses  a  doubly 
contoured  membrane  and  a  large  germinal  spot  (nucleolus),  which 
shows  ameboid  movements. 

The  origin  of  the  zona  pellucida  has  not  as  yet  been  fully  de- 
termined. It  probably  represents  a  product  of  the  egg  epithelium, 
and  may  be  regarded  in  general  as  a  cuticular  formation  of  these 
cells.  At  all  events  it  contains  numerous  small  canals  or  pores  into 
which  the  processes  of  the  cells  composing  the  corona  radiata  ex- 
tend. These  processes  are  to  be  regarded  as  intercellular  bridges 
(Retzius,  90) ;  and,  according  to  Palladino,  they  occur  not  only 
between  the  ovum  and  the"  corona  radiata,  but  also  between  the 
follicular  cells  themselves.  In  the  ripe  human  ovum  the  pores  are 
apparently  absent  (Nagel),  and  it  is  very  probable  that  they  have  to 
do  with  the  passage  of  nourishment  to  the  growing  egg.  Retzius 
believes  that  the  zona  pellucida  is  derived  from  the  processes  of  the 
cells  composing  the  corona  radiata,  which  at  first  interlace  and  form 
a  network  around  the  ovum.  Later,  the  matrix  of  the  membrane  is 
deposited  in  the  meshes  of  the  network,  very  probably  by  the  egg 
itself. 

Further  developmental  changes  are,  however,  necessary  before  a 
fully  developed  ovum  (ripe  ovum)  may  be  fertilized.  These  are 
grouped  under  the  head  of  maturation  of  the  ovum.  They  have  in 
part  been  described  in  a  former  section  (p.  65),  but  may  receive 
further  consideration  at  this  time.  During  maturation  the  chromo- 
somes are  reduced  in  number,  so  that  the  matured  ovum  presents 


312 


THE    GENITOURINARY    ORGANS. 


only  half  the  number  found  in  a  somatic  cell  of  the  same  animal. 
The  manner  in  which  this  reduction  takes  place  has  been  described 
for  many  invertebrates  and  vertebrates,  and  in  all  ova  studied  with 
reference  to  this  point  essentially  the  same  pherrbmena  have  been 
observed.  In  this  account  we  shall  follow  the  process  as  it  occurs 
in  the  Copepoda  (Riickert,  94). 

During  the  period  of  growth  the  cells  composing  the  last  gen- 
eration of  oogonia  (primitive  ova)  increase  in  size,  and  are  then 


Fig.  264.—  Schematic  representation  of  the  behavior  of  the  chromatin  during  the 
maturation  of  the  ovum  (from  Riickert,  94).  Instead  of  12  chromosomes  we  have  drawn, 
for  the  sake  of  simplicity,  only  four  :  a,  a,  a,  First,  and  (b)  second  polar  body. 

known  as  "  oocytes  "  (the  ripe  ova).  These  then  undergo  mitotic 
division,  and  in  each  a  spirem  is  formed  which  divides  into  12 
chromosomes,  and  not  into  24  as  in  the  case  of  the  somatic  cells. 
These  12  chromosomes  split  longitudinally,  so  that  the  germinal 
vesicle  is  seen  to  contain  12  pairs  of  chromosomes/ or  daughter 
loops.  By  this  process  the  oogonia  have  become  egg  mother  cells 
(O.  Hertwig,  90)  or  oocytes  of  the  first  order.  The  loops  now 
begin  to  shorten  and  each  soon  divides  crosswise  into  two  equal 


THE  FEMALE  GENITAL  ORGANS. 


313 


rods,  thus  giving  rise  to  1 2  groups  of  4  chromosomes,  or  1 2  tetrads. 
The  mother  cell  now  divides  into  2  unequal  parts,  the  process  con- 
sisting in  a  distribution  of  the  rods  composing  the  tetrads  in  such  a 
way  that  the  pairs  of  rods  derived  from  one  set  of  daughter  loops 
pass  to  the  one  daughter  cell,  and  those  derived  from  the  other  set 
to  the  second  daughter  cell.  In  this  manner  are  formed  the  large 
egg  daughter  cells  (O.  Hertwig)  or  oocytes  of  the  second  order,  and 
a  smaller  cell,  the  first  polar  body.  From  this  it  is  seen  that  the 
daughter  cell  still  retains  12  pairs  of  rods.  A  second  unequal  division 
immediately  follows  without  a  period  of  rest,  but  in  this  case  the  com- 
ponent parts  of  the  pairs  of  rods  are  so  divided  that  each  separate 
rod  moves  away  from  its  fellow,  although  they  both  originated  from 
the  same  daughter  loop.  In  this  manner  a  cell  of  the  third  gen- 
eration is  formed,  the  oocyte  of  the  third  order,  or  mature  ovum, 
as  well  as  a  second  polar  body.  The  second  division  in  the  period 
of  maturation  is  peculiar  in  that  here  daughter  chromosomes  are 
formed,  not  by  a  longitudinal  splitting  of  the  chromosomes,  but  by 
a  transverse  division. 

In  the  process  of  development  of  the  ova,  three  periods  are 
therefore  distinguishable.  The  first,  or  period  of  proliferation,  rep- 
resents a  stage  of  repeated  mitotic  division  in  the  oogonia,  during 
which  the  latter  become  gradually  reduced  in  size.  In  the  second, 
or  period  of  growth,  the  oogonia  increase  in  size  and  are  then  ready 
for  the  third,  or  period  of  maturation.  In  the  latter,  by  means  of 
a  modified  double  mitotic  division,  uninterrupted  by  any  resting 
stage,  the  matured  ovum  and  the  polar  bodies  are  formed.  These 
several  periods  are  represented  in  figure  265. 

The  manner  in  which  the  fully  developed  Graafian  follicle 
bursts  and  its  ovum  is  freed  is  still  a  subject  of  controversy  ;  the 
following  may  be  said  regarding  it :  By  a  softening  of  the  cells 
forming  the  pedicle  of  the  discus  proligerus,  the  latter,  together 
with  the  ovum,  are  separated  from  the  remaining  granulosa,  and  lie 
free  in  the  liquor  folliculi.  At  the  point  where  the  follicle  comes  in 
contact  with  the  tunica  albuginea  of  the  ovary,  the  latter,  with  the 
theca  folliculi,  becomes  thin,  and  in  this  region,  known  as  the 
stigma,  the  blood-vessels  are  obliterated  and  the  entire  tissue  grad- 
ually atrophies  ;  thus  a  point  of  least  resistance  is  formed  which  gives 
way  at  the  slightest  increase  in  pressure  within  the  follicle,  or  in  its 
neighborhood. 

The  increase  of  pressure  within  the  follicle,  leading  to  its  rup- 
ture, is,  according  to  Nagel  (96),  due  to  a  thickening  of  the  tunica 
interna  of  the  theca  of  the  follicle.  The  cells  of  this  layer  prolif- 
erate and  increase  in  size  and  show  yellowish  colored  granules. 
This  cell-proliferation  leads  to  a  folding  of  the  tunica  interna,  the  folds 
encroaching  on  the  cavity  of  the  follicle,  and  causing  its  contents  to 
be  pushed  toward  the  stigma. 

When  the  ovum  is  released,  the  rest  of  the  follicle  remains  be- 
hind to  form  a  corpus  luteuin.  In  the  formation  of  the  much  larger 


314  THE    GENITOURINARY    ORGANS. 

corpus  luteum  verum — i.  e.,  one  whose  ovum  has  been  fertilized  and 
is  in  process  of  further  development — the  regressive  metamorphosis  is 
much  slower  than  is  the  case  with  the  corpora  lutea  spuria, whose  ova 
have  not  been  impregnated.  In  place  of  the  liquor  folliculi  the  corpus 
luteum  usually  contains  a  blood  coagulum  which  is  formed  as  a  result 
of  the  rupture  of  the  adjacent  blood-vessels.  Then  follows  a  prolifera- 
tion of  the  tissue  composing  the  tunica  interna  of  the  theca  folliculi. 
This  ingrowth  gradually  surrounds  and  finally  penetrates  into  the 
coagulum  and  the  few  granulosa  cells  remaining,  while  the  latter 
degenerate  and  are  eventually  absorbed.  The  proliferating  tissue 
contains  cells  filled  with  pigment,  the  lutein  cells,  and  it  is  these 
which  give  rise  to  the  characteristic  yellow  color  of  the  bodies. 
The  inner  wall  of  the  corpus  luteum  is 'gradually  folded  in  and  the 

Primordial  egg-cell. 


Germinal  zone. 

/Zone  of  mitotic  division. 
\  /      \  /     (The  number  of  genera- 

I  I        \  l      tions  is  much  larger  than 

here  represented.) 


^  Zone  of  growth. 

•    m± 

Oocyte  1.  order. 

Oocyte  II.  order. ^^^B  V    I-   P- B.      /Zone  of  maturation. 

Matured  ovum. 


r,  A 


II.   P.B. 

Fig.  265. — Scheme  of  the  development  and  maturation  of  an  ascaris  ovum  (after  Boveri)  : 
P.  B.,  Polar  bodies.     (From  "  Ergebn.  d.  Anat.  u.  Entw.,"  Bd.  I.) 

degenerating  central  portion  is  finally  penetrated  by  vessels  and 
absorbed  by  the  proliferating  cells  from  the  outer  wall.  In  the  folds 
of  the  tunica  interna,  composed  of  lutein  cells,  there  is  found  a  vari- 
able amount  of  fibrous  connective  tissue  carrying  blood-vessels 
which  break  up  into  capillaries,  the  latter  penetrating  between  the 
lutein  cells. 

According  to  Sobotta  (96  and  97),  the  corpus  luteum  of  both 
the  mouse  and  the  rabbit  is  formed  chiefly  by  a  hypertrophy  of  the 
epithelial  cells,  while  the  vascular  connective  tissue  of  the  inner 
thecal  layer  penetrates  between  the  epithelial  cells  in  the  shape  of 
processes  accompanied  by  leucocytes,  which  form  a  cellular  net- 
work around  the  central  coagulum.  The  blood  is  finally  absorbed 


THE    FEMALE    GENITAL   ORGANS. 


315 


without  the  formation  of  hematoidin  crystals,  and  a  mucoid  con- 
nective-tissue mass  is  the  result.  There  is  then  no  further  prolifera- 
tion of  connective  tissue  and  the  corpus  luteum  is  fully  developed 
in  this  condition.  Later,  fat  globules  are  deposited  in  the  greatly 
enlarged  epithelial  cells.  In  the  mouse  there  is  no  difference  as 
to  structure  or  size  between  corpora  lutea  derived  from  follicles 
whose  ova  have  been  impregnated  and  those  whose  ova  have  not 
been  fertilized. 

After  a  variable  time  the  tissue  of  the  corpus  luteum  itself 
undergoes  hyaloid  degeneration,  a  process  which  may  be  compared 
to  the  formation  of  scar  tissue,  and  which  finally  results  in  the 
formation  of  the  corpus  albicans.  The  latter  is  then  in  its  turn 


Membrana 
granulosa. 


Discus 
proligerus. 

^•Ovum. 


Germinal  vesicle. 


"^Blood-vessel. 

Fig.  266. — Section  of  fully  developed  Graafian  follicle  from  injected  ovary  of  pig ; 

X50. 


absorbed,  and  in  the  end  there  remains  in  its  place  only  a  connec- 
tive tissue  containing  very  few  fibers. 

Not  all  of  the  eggs  and  follicles  reach  maturity ;  very  many 
are  destroyed  by  a  regressive  process  known  as  atresia  of  the  fol- 
licles. This  process  may  begin  at  any  stage,  even  affecting  the 
primitive  ova  while  still  imbedded  in  the  germinal  epithelium — first 
attacking  the  egg  itself  and  later  the  surrounding  follicular  epithe- 
lium, although  in  both  the  degenerative  process  is  identical.  The 
germinal  vesicle  and  the  nuclei  of  the  follicular  cells  usually 
undergo  a  chromatolytic  degeneration,  although  they  sometimes 
disappear  without  apparent  chromatolysis  (direct  atrophy),  while 


316  THE    GENITOURINARY    ORGANS. 

the  cell-bodies  are  generally  subjected  to  a  fatty  degeneration  or 
may  even  undergo  what  is  known  among  pathologists  as  an  albu- 
minous degeneration — L  e.,  one  characterized  by  granulation  and 
showing  no  fat  reaction  but  numerous  reactions  such  as  are  ob- 
served where  albumin  is  present.  These  two  forms  of  metamor- 
phosis result  in  a  liquefaction  of  the  cell-body,  and  finally  lead  to 
a  hyaline  swelling,  which  renders  the  substance  of  the  cell  homo- 
geneous. The  zona  pellucida  softens,  increases  in  volume,  becomes 
wrinkled,  and  after  some  time  is  absorbed.  A  further  stage  in 
the  regressive  process  consists  in  the  formation  of  scar  tissue,  as 
in  the  case  of  the  corpus  luteum.  Here  leucocytes  accompany 
the  proliferation  from  the  tunica  interna  of  the  theca  folliculi,  and 
assist  in  absorbing  the  products  of  degeneration,  the  result  being 
a  connective-tissue  scar  (vid.  G.  Ruge,  and  Schottlander,  91,  93). 

The  blood-vessels  of  the  ovary  enter  at  the  hilum  and  branch 
in  the  medullary  substance  of  the  ovary.  From  these  medullary 
vessels  branches  are  given  off  which  penetrate  the  follicular  zone, 
giving  off  branches  to  the  follicles  and  terminating  in  a  capillary 
network  in  the  tunica  albuginea  (Clark,  1900).  The  relations  of 
the  branches  to  the  follicles  are  such  that  in  the  outer  layer  of  the 
theca  folliculi  the  vessels  form  a  network  with  wide  meshes  while 
the  inner  layer  contains  a  fine  capillary  network  (Fig.  266).  The 
veins  are  of  large  caliber  and  form  a  plexus  at  the  hilum  of  the 
ovary. 

The  lymphatics  of  the  ovary  are  numerous.  They  begin  in 
clefts  in  the  follicular  zone,  which  unite  to  form  vessels  lined  by 
endothelial  cells  in  the  medulla.  They  leave  the  ovary  at  the 
hilum. 

The  nerves  accompany  and  surround  the  blood-vessels,  while 
very  few  nerve-fibers  penetrate  into  the  theca  folliculi ;  those  doing 
so  form  a  network  around  the  follicle  and  end  often  in  small  nodules 
without  penetrating  beyond  the  theca  itself.  Ganglion  cells  of  the 
sympathetic  type  also  occur  in  the  medulla  of  the  ovary  near  the 
hilum  (Retzius,  93  ;  Riese,  Gawronski). 


3.  THE  FALLOPIAN  TUBES,  UTERUS,  AND  VAGINA. 

The  Fallopian  tubes  consist  of  a  mucous  membrane,  muscular 
coat,  and  peritoneal  covering. 

The  mucous  membrane  presents  a  large  number  of  longitudinal 
folds  which  frequently  communicate  with  one  another.  Very  early 
in  the  development  four  of  these  folds  are  particularly  noticeable  in 
the  isthmus  ;  these  may  also  be  recognized  at  times  in  the  adult. 
These  are  the  chief  folds,  in  contradistinction  to  the  rest,  which  are 
known  as  the  accessory  folds  (Frommel).  The  accessory  folds  are 
well  developed  in  the  isthmus,  and  are  here  so  closely  arranged 
that  no  lumen  can  be  seen  with  the  naked  eye.  The  epithelium 
lining  the  tubes  is  composed  of  a  single  layer  of  ciliated  columnar 


THE    FEMALE    GENITAL    ORGANS. 


317 


cells  which  entirely  cover  the  folds  as  well  as  the  tissue  between 
them.  Glands  do  not  occur  in  the  oviducts,  unless  the  crypts 
between  the  folds  may  be  considered  as  such.  The  mucosa 
beneath  the  epithelium  contains  relatively  few  connective-tissue 
fibers,  but  numerous  cellular  elements.  In  the  isthmus  it  is  com- 
pact, but  in  the  ampulla  and  infundibulum  its  structure  is  looser. 
The  mucosa  contains  a  few  nonstriated  muscle-fibers,  which  have  a 
longitudinal  direction  and  extend  into  the  chief  folds,  but  not  into 
the  accessory  folds. 

External  to  the  mucosa  is  found  the  muscular  coat,  consisting 
of  an  inner  circular  and  an  outer  and  thinner  longitudinal  layer. 
The  latter  is  imperfectly  developed  in  the  ampulla  and  may  be 


_.  Mucosa. 


Crypt.  — 


_   Crypt. 


Fig.  267.— Section  of  oviduct  of  young  woman.     To  the  left  and  above  are  two 
enlarged  ciliated  epithelial  cells  from  the  same  tube  ;  X  I7°- 


entirely  absent  in  the  infundibulum.  The  peritoneal  layer  consists 
of  a  loose  connective  tissue  covered  by  mesothelium. 

The  uterus  is  composed  of  a  mucous,  a  muscular,  and  a  peri- 
toneal coat. 

The  mucosa  of  the  body  of  the  uterus  and  cervix  is  lined  by  a 
single  layer  of  columnar  ciliated  epithelial  cells  ;  these  are  some- 
what higher  in  the  cervix  than  in  the  corpus.  Barfurth  (96)  has 
found  intercellular  bridges  between  the  cells  of  the  uterine  epithelium 
in  the  guinea-pig  and  rabbit.  In  the  cervix  of  the  virgin  the  ciliated 
columnar  epithelium  extends  as  far  as  the  external  os,  at  which 
point  this  usually  changes  to  a  stratified  squamous  epithelium.  In 


318  THE    GENITOURINARY    ORGANS. 

multipart  the  squamous  epithelium  extends  into  the  cervical  canal 
and  may  be  found,  with  occasional  exceptions  (islands  of  ciliated 
epithelium),  throughout  its  entire  lower  third.  This  arrangement 
is  subject  to  considerable  variation,  so  that  even  in  children  the 
lower  portion  of  the  cervical  canal  may  sometimes  be  lined  by 
stratified  epithelium.  In  the  body  of  the  uterus  the  mucosa  is  com- 
posed of  a  reticular  connective  tissue,  resembling  in  structure  that 
of  the  mucosa  of  the  intestinal  canal.  This  reticular  connective 
tissue  consists  of  connective-tissue  fibers  and  branched  connective- 
tissue  cells  arranged  in  the  form  of  a  network,  in  the  meshes  of 
which  are  found  lymphocytes  and  leucocytes.  Tile  mucosa  of  the 
cervix  is  somewhat  denser,  containing  more  fibrous  tissue. 

In  the  cervical  canal  the  mucosa  of  the  anterior  and  posterior 
walls  is  elevated  to  form  numerous  folds,  extending  laterally  from 
larger  median  folds.  These  folds  are  known  as  the  plicce  palniatce. 
The  mucosa  of  the  body  of  the  uterus  and  of  the  cervix  contains 
numerous  glands,  the  uterine  and  cervical  glands.  The  uterine 
glands  are  branched  tubular  in  type,  and  extend  through  the 
mucosa  and  for  a  short  distance  into  the  muscular  layer.  They  are 
lined  by  ciliated  columnar  epithelium,  resting  on  a  basement  mem- 
brane. The  cervical  glands  are  of  the  same  shape  and  structure. 
Above  the  plicae  palmatae  the  glands  are  numerous  ;  below,  they 
gradually  diminish  in  number.  Besides  these  glands  the  cervix 
also  contains  peculiar  short  crypts  with  lateral  sacculations,  the 
lumina  of  which  are  wider  and  the  epithelium  higher  than  in  the 
cervical  glands.  The  glands  and  crypts  extend  as  far  as  the  ex- 
ternal os.  In  the  mucous  membrane  of  the  cervical  region  we 
find  peculiar,  closed  sacs  of  varying  size  lined  by  simple  cylindric 
or  ciliated  epithelium,  the  so-called  ovula  Nabothi,  which  probably 
represent  cystic  formations  (vid.  A.  Martin). 

It  has  been  the  opinion  of  most  gynecologists  hitherto  that  the 
ciliary  movement  of  the  epithelium  in  the  oviducts  and  uterus  was 
in  the  direction  of  the  tubo-uterine  opening  ;  but  later  investiga- 
tions have  established  the  fact  that  in  both  the  uterus  and  oviducts 
the  general  direction  of  the  wave-like  ciliary  motion  is  toward  the 
vagina  (Hofmeier). 

Three  layers  of  muscular  tissue  are  to  be  seen  both  in  the 
corpus  and  cervix  uteri — an  inner  longitudinal,  a  middle  nearly  cir- 
cular, in  which  the  principal  blood-vessels  are  found,  and  an  outer 
longitudinal.  The  inner  and  outer  layers  are  known  respectively 
from  their  position  as  the  stratum  mucosum  and  stratum  serosum, 
the  middle  and  more  vascular  as  the  stratum  vasculosum.  As  com- 
pared with  the  middle,  the  inner  and  outer  muscle  layers  are 
poorly  developed.  The  complicated  conditions  found  in  the  uterine 
musculature  can  be  better  understood  if  some  attention  be  paid  to 
its  origin.  The  circular  layer  should  be  regarded  as  the  original 
musculature  of  the  Mullerian  ducts.  The  outer  longitudinal  layer 
develops  later,  and  is  derived  from  the  musculature  of  the  broad 


THE    FEMALE    GENITAL    ORGANS. 


319 


ligament.  Between  these  two  are  the  large  vessels  accompanied 
by  a  certain  amount  of  muscular  tissue — a  condition  which  persists 
throughout  life  in  the  carnivora.  In  man  the  blood-vessels  pene- 
trate into  the  circular  musculature  and  only  appear  later  in  the 
inner  muscular  layer.  A  true  muscularis  mucosae  is  not  present  in 
the  human  uterus  (Sobotta,  91). 

The  serous  or  peritoneal  layer  consists  of  a  layer  of  mesothelial 
cells  and  submesothelial  connective  tissue. 

The  uterus  derives  its  blood  supply  from  the  uterine  and  ovarian 
arteries,  which  enter  from  the  broad  ligament  through  its  lateral 
portion.  These  vessels  pass  to  the  stratum  vasculosum  of  the 
muscular  layer,  where  they  branch  repeatedly,  some  of  the  branches 


Uterine 
epithelium. 


-  Gland. 


-    Mucosa. 


Fig.  268. — From  uterus  of  young  woman;   X  34-      (From  a  preparation  by  Dr. 

J.  Amann.) 


entering  the  mucosa,  where  they  form  capillary  networks  surround- 
ing the  glands  and  a  dense  capillary  network  situated  under  the 
uterine  epithelium.  The  veins  form  a  venous  plexus  in  the  deeper 
portion  of  the  mucosa,  especially  well  developed  in  the  cervix  and 
os  uteri.  From  this  plexus  the  blood  passes  to  a  second  well- 
developed  venous  plexus  situated  in  the  stratum  vasculosum  of  the 
muscular  layer,  whence  the  blood  passes  to  the  plexus  of  uterine 
and  ovarian  veins. 

The  lymphatics  begin  in  numerous  clefts  in  the  uterine  mucosa ; 


320 


THE    GENITOURINARY    ORGANS. 


from  here  the  lymph  passes  by  way  of  lymph-vessels  to  the  mus- 
cular coat,  between  the  bundles  of  which  are  found  numerous 
lymph-vessels  especially  in  the  middle  or  vascular  layer.  These 
lymph-vessels  terminate  in  larger  vessels  found  in  the  subserous 
connective  tissue. 

The  uterus  and  Fallopian  tubes  receive  numerous  medullated  and 
nonmedullated  nerves.  The  latter  terminate  in  the  muscular  layers. 
Medullated  fibers  have  been  traced  into  the  mucosa,  where  they 
form  plexuses  under  the  epithelium,  from  which  branches  have  been 
traced  between  the  epithelial  cells  and  between  the  gland-cells.  In 
the  course  of  the  nerves  ganglion  cells  of  the  sympathetic  type 
have  been  observed. 


Fig.  2by. — From  section  of  human  vagina. 

In  the  vagina  we  distinguish  also  three  coats — the  mucous 
membrane,  the  muscular  layer,  and  the  outer  fibrous  covering. 

The  epithelium  of  the  mucous  membrane  is  of  the  stratified 
squamous  type,  and  possesses,  as  usual,  a  basal  layer  of  cylindric 
cells.  The  mucosa  of  the  vagina  consists  of  numerous  connective- 
tissue  fibers  mingled  with  a  number  of  exceptionally  coarse  elastic 
fibers.  Papillae  containing  blood-vessels  are  present  everywhere  ex- 
cept in  the  depressions  between  the  columnar  rugarum.  It  is  generally 
stated  that  the  vagina  has  no  glands,  but  according  to  the  observa- 
tions of  von  Preuschen  and  C.  Ruge,  a  few  isolated  glands  occur  in 


THE    FEMALE    GENITAL   ORGANS. 


321 


the  vagina.  They  are  relatively  simple  in  structure,  form  irregular 
tubes,  and  are  lined  by  ciliated  columnar  epithelium.  The  excre- 
tory ducts  are  lined  by  stratified  squamous  epithelium.  Diffuse 
adenoid  tissue  is  met  with  in  the  mucosa,  which  sometimes  assumes 
the  form  of  lymphatic  nodules. 

The  muscular  coat,  which  in  the  lower  region  is  quite  prominent, 
may  be  separated  indistinctly  into  an  outer  longitudinal  and  an  in- 
ner circular  layer  ;  the  latter  is,  as  a  rule,  poorly  developed,  and  may 
be  entirely  absent.  The  muscular  coat  is  especially  well  developed 
anteriorly  in  the  neighborhood  of  the  bladder. 


Fig.  270.  — From  section  of  human  labia  minora. 

The  outer  fibrous  layer  consists  of  dense  connective  tissue 
loosely  connected  with  the  adjacent  structures. 

At  its  lower  end  the  vagina  is  partially  closed  by  the  hymen 
which  must  be  regarded  as  a  rudiment  of  the  membrane  which  in 
the  embryo  separates  the  lower  segment  of  the  united  Miillerian 
ducts  from  the  ectoderm  of  the  sinus  urogenitalis.  Accordingly, 
the  epithelium  on  the  inner  surface  of  the  hymen  partakes  of  the 
character  of  the  vaginal  epithelium  ;  that  on  the  outer  surface  re- 
sembling the  skin  in  structure  (G.  Klein). 


21 


322  THE    GENITOURINARY    ORGANS. 

The  epithelium  of  the  vestibulum  gradually  assumes  the  char- 
acteristics of  the  epidermis  ;  its  outer  cells  lose  their  nuclei  and 
sebaceous  glands  occur  here  and  there  in  the  neighborhood  of  the 
urethral  orifice  and  on  the  labia  minora.  Hair  begins  to  appear  on 
the  outer  surface  of  the  labia  majora. 

The  clitoris  is  covered  by  a  thin  epithelial  layer,  resembling  the 
epidermis.  This  rests  on  a  fibrous-tissue  mucosa  having  numerous 
papillae,  some  of  which  contain  capillaries,  others  special  nerve- 
endings.  In  the  clitoris  of  the  adult  no  glands  are  found.  The 
greater  portion  of  the  clitoris  consists  of  cavernous  tissue,  homol- 
ogous to  the  corpora  cavernosa  of  the  penis  ;  the  corpus  spongi- 
osum  is  not  present  in  the  clitoris. 

The  glands  of  Bartholin  the  homologues  of  the  glands  of 
Cowper  in  the  male,  are  mucous  glands  situated  in  the  lateral 
walls  of  the  vestibule  of  the  vagina.  The  terminal  portions  of 
their  ducts  are  lined  by  stratified  squamous  epithelium. 

Free  sensory  nerve-endings,  with  or  without  terminal  enlarge- 
ments, have  been  demonstrated  in  the  epithelium  of  the  vagina 
(Gawronski).  The  sensory  nerve-fibers  form  plexuses  in  the 
mucosa,  and  lose  their  medullary  sheaths  as  they  approach  the 
epithelium.  Sympathetic  ganglia  are  met  with  along  the  course  of 
these  nerves,  and  nonmedullated  nerves  terminate  in  the  involuntary 
muscular  tissue  of  the  vaginal  wall. 

In  the  connective-tissue  papillae  and  in  the  deeper  portions  of  the 
mucosa  of  the  glans  clitoridis  are  found,  besides  the  ordinary  type 
of  tactile  corpuscles  and  the  spherical  end-bulbs  of  Krause,  the  so- 
called  genital  corpuscles  .(see  p.  155).  Numerous  Pacinian  cor- 
puscles have  been  observed  in  close  proximity  to  the  nerve-fibers 
of  the  clitoris  and  the  labia  minora. 


In  varying  regions  of  the  medullary  substance  of  the  ovary, 
but  more  usually  in  the  neighborhood  of  the  hilum,  there  occur 
irregular  epithelial  cords  or  tubules  provided  with  columnar  epithe- 
lium, ciliated  or  nonciliated,  which  constitute  the  paroophoron. 
These  are  the  remains  of  the  mesonephros,  and  are  continuations 
of  that  rudimentary  organ — the  epoophoron — of  similar  structure 
which  lies  within  the  broad  ligament.  The  separate  tubules  of  the 
epoophoron  communicate  with  the  dtict  of  Gartner  (Wolffian  duct), 
which  in  the  human  being  is  short,  ends  blindly,  and  never,  as  in 
certain  animals,  opens  into  the  lower  portion  of  the  vagina.  These 
derivatives  of  the  primitive  kidney  consist  of  blindly  ending  tubules 
of  varying  length  lined  by  a  ciliated  epithelium,  the  cells  of  which 
are  often  found  in  process  of  degeneration. 

The  hydatids  of  Morgagni  are  duplications  of  the  peritoneum. 


THE    MALE   GENITAL   ORGANS.  323 


D*  THE  MALE  GENITAL  ORGANS. 

J.  THE  SPERMATOZOON. 

The  semen,  or  sperma,  is  a  fluid  that,  as  a  whole,  consists  of 
the  secretion  of  several  sets  of  glands  in  which  the  sexual  cells,  the 
spermatosomes,  or  spermatozoa,  which  are  formed  in  the  testes,  are 
suspended. 

We  shall  first  consider  the  structure  of  the  typical  adult  sperma- 
tosome,  taking  up  consecutively  its  component  parts.  Three  prin- 
cipal parts  may  be  distinguished — the  head,  the  middle  piece,  and 
the  tail  or  flagellum.  The  round  or  oval  body  of  the  head  termi- 
nates in  a  lanceolate  extremity.  The  former  consists  of  chromatin, 
and  is  most  intimately  associated  with  the  phenomenon  of  fertiliza- 
tion. The  middle  piece,  which  is  attached  to  the  posterior  end  of 
the  head,  is  composed  of  a  protoplasmic  envelop  which  surrounds  a 
portion  of  the  so-called  axial  thread.  The  latter  is  enlarged  ante- 
riorly just  behind  the  head  to  form  the  terminal  nodule,  which  fits  into 
a  depression  in  the  head.  From  the  middle  piece  on,  the  axial  thread 


Fig.  271.— Diagram  showing  the  general  characteristics  of  the  spermatozoa  of 
various  vertebrates :  a,  Lance ;  b,  segments  of  the  accessory  thread  ;  c,  accessory 
thread  ;  d,  body  of  the  head ;  e,  terminal  nodule  ;  f,  middle  piece  ;  g,  marginal  thread ; 
h,  axial  thread  ;  z,  undulating  membrane  ;  k,  fibrils  of  the  axial  thread  ;  /,  fibrils  of  the 
marginal  thread ;  m,  end  piece  of  Retzius  ;  n,  rudder-membrane. 

is  continued  into  the  tail  of  the  spermatozoon,  and  is  here  sur- 
rounded by  a  transparent  substance — the  sheath  of  the  axial  thread. 
The  envelop  is  lacking  at  the  posterior  extremity  of  the  tail,  where 
the  axial  thread  extends  for  a  short  distance  as  a  naked  filament 
called  the  end-piece  of  Retzius.  From  the  middle  piece  a  still  finer 
thread  is  given  off,  the  marginal  thread,  which  extends  at  a  certain 
distance  from  the  axial  thread  as  far  as  the  end-piece  of  Retzius. 
In  its  course  it  crosses  and  recrosses  the  axial  thread  at  various 
points,  and  may  even  wind  around  it  in  a  spiral  manner.  In  all  in- 
stances it  is  connected  with  the  sheath  of  the  axial  thread  by  a 
delicate  membrane — the  undulating  membrane.  Another  and  still 
more  delicate  filament — the  accessory  thread — runs  parallel  with  the 
axial  thread  along  the  surface  of  its  sheath  and  terminates  at  a  cer- 
tain distance  from  the  end -piece  of  Retzius.  Near  the  extremity  of 
the  flagellum  and  immediately  in  front  of  the  end-piece  is  another 
and  shorter  membrane, — the  rudder  membrane, — which  is  continu- 
ous with  the  undulating  membrane.  Maceration  reveals  a  fibrillar 


324 


THE    GENITOURINARY    ORGANS. 


--   d 


structure  of  both  the  axial  and  marginal  threads  (Ballowitz),  while 
the  accessory  thread  is  separated  into  a  number  of  short  segments. 
In  mammalia,  and  especially  in  man,  the 
spermatozoa  seem  to  be  more  simply  con- 
structed. Here  the  head  is  pyriform,  and 
somewhat  flattened,  with  a  slight  ridge  along 
the  depression  at  either  side  of  its  anterior 
thinner  portion  (Fig.  272).  In  some  mammalia 
(mouse),  the  head  is  provided  with  a  so- 
called  cap,  which  corresponds  to  the  lance 
previously  mentioned.  The  middle  piece  is 
relatively  long  and  shows  a  distinct  cross- 
striation,  which  may  be  attributed  to  its  spiral 
structure.  Here  also  the  middle  piece  is  tra- 
versed by  the  axial  thread,  which  ends  at  the 
head  in  a  terminal  nodule,  and  may  be  sep- 
arated as  in  other  mammalia  into  a  number 
of  fibrils.  Some  years  ago  Gibbes  described 
an  undulating  membrane  in  the  human  sper- 
matozoon, an  observation  which  was  confirmed 
by  W.  Krause  (81).  The  head  of  the  human 
spermatosome  is  from  3  //  to  5  p.  long,  and 
from  2  fjt  to  3  p.  in  breadth  ;  the  middle  piece 
is  6  fJL  long  and  I  /2  in  breadth  ;  the  tail  is  from 
40  fj.  to  60 //  long,  and  the  end-piece  6  p.  long. 
The  spermatozoa  are  actively  motile,  a  phe- 
nomenon due  to  the  flagella,  which  give  them 
a  spiral,  boring  motion.  They  are  character- 
ized by  great  longevity  and  are  very  resistant 
to  the  action  of  low  temperatures  (vid.  Pier- 
sol,  83).  In  some  species  of  bat  the  sper- 
matozoa penetrate  into  the  oviduct  of  the 
female  in  the  fall,  but  do  not  contribute  to  im- 
pregnation until  the  spring,  when  the  ova  mature.  (For  the 
structure  of  the  spermatosomes  see  Jensen,  Ballowitz.) 


Fig.  272. — Human 
spermatozoa.  The  two 
at  the  left  after  Retzius 
(81)  ;  the  one  at  the 
extreme  left  is  seen  in 
profile ;  the  other  in 
surface  view  ;  the  one 
at  the  right  is  drawn  as 
described  by  Jensen  :  <?, 
Head  ;  b,  terminal  nod- 
ule ;  c ,  middle  piece  ; 
J,  tail  ;  e,  end-piece  of 
Retzius. 


2.  THE  TESTES. 

The  testis  is  inclosed  within  a  dense  fibrous  capsule, — the 
tunica  albuginea,- — about  one-sixteenth  of  an  inch  in  thickness,  and 
surrounded  by  a  closed  serous  sac,  derived  from  the  peritoneum 
during  the  descent  of  the  testes,  and  therefore  lined  by  mesothelial 
cells.  This  serous  sac — the  tunica  vaginalis — consists  of  a  visceral 
layer  attached  to  the  tunica  albuginea,  and  a  parietal  layer  which 
blends  with  the  scrotum.  The  cavity  contains  normally  a  small 
amount  of  serous  fluid.  On  the  inner  surface  of  the  tunica  albuginea 
is  found  a  thin  layer  of  loose  fibrous  tissue  containing  blood-vessels 
— the  tunica  vasculosa.  The  tunica  albuginea  is  thickened  in  its 


THE    MALE    GENITAL    ORGANS. 


325 


posterior  portion  to  form  the  mediastinum  testis,  or  the  corpus 
HigJutiori,  which  projects  as  a  fibrous-tissue  ridge  for  a  variable 
distance  into  the  substance  of  the  testis.  The  gross  structure  of  the 
testis  is  best  seen  in  a  sagittal  longitudinal  section.  Even  a  low 
magnification  will  show  that  the  testis  is  composed  of  lobules.  These 
are  produced  by  septa  which  extend  into  the  substance  of  the  organ 
and  are  derived  from  the  investing  tunics  of  the  testis  and  diverge  in 
a  radiate  manner  from  the  mediastinum  testis.  The  lobules  are  of 
pyramidal  shape,  with  their  bases  directed  toward  the  capsule  and 
their  apices  toward  the  mediastinum.  They  consist  principally  of 
the  seminiferous  tubules,  whose  transverse,  oblique,  and  longitudinal 


Lobule  of  testis.      Tunica  albuginea. 


Caput  epidi- 
dymidis. 


Corpus  Highmori 
and  rete  testis. 


Blood-vessel. 


Tubuli  recti. 


Vasepididymidis. 


Fig.  273. — Longitudinal  section  through  human  testis  and  epididymis.     The  light  areas 
between  the  lobules  are  the  fibrous- tissue  septa  of  the  testis ;  X  2« 


sections  may  be  observed  in  sections  of  the  testis.  When  isolated, 
these  tubules  are  seen  to  begin  in  the  testis  as  closed  canals,  which 
are  closely  coiled  upon  each  other  (convoluted  tubules)  and  describe 
a  tortuous  course,  until  they  finally  reach  the  corpus  Highmori. 
Immediately  before  they  reach  the  latter,  the  convoluted  tubules 
change  into  short,  straight  and  narrow  segments — the  straight 
tubides,  or  tnbnli  recti.  Within  the  corpus  Highmori,  all  the  straight 
tubules  of  the  testis  unite  to  form  a  tubular  network — the  rcte  testis 
(Haller). 

From  this  network  about  fifteen  tubules — the  vasa  effercntia — 


326  THE    GENITOURINARY    ORGANS. 

arise.  The  latter,  at  first  straight,  soon  begin  to  wind  in  such  a  man- 
ner that  the  various  convolutions  of  each  canal  form  an  independent 
system,  invested  by  a  fibrous  sheath  of  its  own — coni  vasculosi 
Halleri.  These  lobules  constitute  the  elements  of  the  globus  major 
of  the  epididymis.  In  cross-section  the  vasa  efTerentia  are  seen  to 
be  stellate  in  shape.  The  vasa  efferentia  gradually  unite  to  form 
one  canal — the  vas  epididymidis.  This  is  markedly  convoluted  and 
is  situated  in  the  body  and  tail  of  the  epididymis  itself. 

The  epithelium  of  the  convoluted  seminiferous  tubules  consists 
of  sustentacular  cells  (cells  or  columns  of  Sertoli)  and  of  sperma- 
togenic  elements.  The  former  are  high,  cylindric  structures  (see 
below),  the  basilar  surfaces  of  which  are  in  contact.  They  do  not 
form  a  continuous  layer,  but  their  basal  processes  are  interwoven 
to  form  a  superficial  network  surrounding  the  epithelium  of  the 


Fig.  274.  Fig.  275. 

Sustentacular  cells  (cells  of  Sertoli)  of  the  guinea-pig  (chrome- silver  method). 
Figure  274,  surface  view  of  the  seminiferous  tubules  ;  figure  275,  profile  view  ;  X  22O: 
#,  Basilar  surface  of  a  cylindric  sustentacular  cell ;  b,  flattened  sustentacular  cell  ;  c,  c, 
depressions  in  the  sustentacular  cells  due  to  pressure  from  the  spermatogenic  cells  ;  d, 
basilar  portion  of  sustentacular  cells. 

seminiferous  tubules.  (Fig.  275.)  In  the  meshes  of  the  reticulum 
are  deposited  numbers  of  plate-like  cells,  which  lie  in  contact  with 
the  basement  membrane  and  also  represent  sustentacular  elements 
(vid.  Merkel,  71). 

Between  the  sustentacular  cells  are  found  from  four  to  six  rows 
of  cells,  possessing  relatively  large  nuclei,  rich  in  chromatin,  and 
derived  from  cells  of  the  deeper  strata  by  mitotic  cell  division.  The 
epithelium  of  the  convoluted  portion  of  the  seminiferous  tubules  is, 
therefore,  a  stratified  epithelium.  The  cells  of  this  epithelium 
present  various  peculiarities  according  to  their  stage  of  development, 
and  will  be  considered  more  fully  in  discussing  spermatogenesis. 
Externally,  the  walls  of  the  convoluted  tubules  are  limited  by  a 
single  layer  or  several  layers  of  spindle-shaped,  epithelioid  cells.  A 
basement  membrane  is  present,  but  very  thin,  and  in  some  cases 


THE  MALE  GENITAL  ORGANS. 


327 


hardly  capable  of  demonstration.  The  convoluted  tubules  are 
separated  from  each  other  by  a  small  amount  of  connective  tissue, 
in  which,  in  addition  to  the  vessels,  nerves,  etc.,  are  found  peculiar 
groups  of  large  cells  containing  large  nuclei,  and  known  as  interstitial 
cells.  Nothing  definite  is  known  regarding  the  significance  of  these 
cells  ;  but  they  are  probably  remains  of  the  Wolffian  body.  Reinke 
(96)  found  repeatedly  crystalloids  of  problematic  significance  in  the 
interstitial  cells  of  the  normal  testis. 

The  stratified  epithelium  of  the  convoluted  tubules  changes  in 


Fig.  276. — From  section  of  human  testis,  showing  convoluted  seminiferous 

tubules. 


the  tubuli  recti  to  an  epithelium  consisting  of  a  single  layer  of  short 
columnar  or  cubical  cells  resting  on  a  thin  basement  membrane. 

The  canals  of  the  rete  testis  (Haller)  are  lined  by  nonciliated 
epithelium,  which  varies  in  type  from  flat  to  cubical.  Communicat- 
ing with  the  rete  testis  is  a  blind  canal,  the  vas  aberrans  of  the  rete 
testis,  lined  with  ciliated  epithelium. 

The  vasa  efferentia  are  lined  partly  by  ciliated  columnar  and 
partly  by  nonciliated  cubical  epithelium.  The  two  varieties  form 
groups  which  alternate,  giving  rise  to  nonciliated  depressions, 
which  represent  gland-like  structures  (Schaffer,  92),  but  do  not 


328 


THE    GENITO-URINARY    ORGANS. 


cause  corresponding  evaginations  of  the  mucosa.  Outside  of  the 
mucosa,  which  consists  of  fibrous  connective  tissue,  there  are  found 
several  layers  of  nonstriated  muscle-fibers  circularly  disposed. 

The  vas    epididymidis   is   lined  by  stratified  ciliated  columnar 
epithelium,   resting   on  a  thin   mucosa,  outside  of  which  there   is 


Fig.  277. — Section  through  human  vasa  efferentia  :    a,  Glands;  b,  ciliated  epithelium 
c,  glandular  structure  ;  d,  connective  tissue. 


Fig.  278. — Cross-section  of  vas  epididymidis  of  human  testis. 

found  an   inner   circular  and   an  outer,  though  thin,  longitudinal 
layer  of  nonstriated  muscular  tissue. 

An  aberrant  canaliculus  also  communicates  with  the  vas  epi- 
didymidis, and  is  here  known  as  the  vas  aberrans  Halleri.     Num- 


THE    MALE    GENITAL   ORGANS. 


329 


bers  of  convoluted  and  blindly  ending  canaliculi  are  frequently 
found  imbedded  in  the  connective  tissue  around  the  epididymis. 
These  constitute  the  paradidymis,  or  organ  of  Gir aides. 

The  blood-vessels  of  the  testis  spread  out  in  the  corpus  High- 
mori  and  in  the  tunica  vasculosa  of  the  connective-tissue  septa  and 
of  the  tunica  albuginea,  their  capillaries  encircling  the  seminal  tu- 
bules in  well-mar.ked  networks. 

The  lymphatic  vessels  begin  in  clefts  in  the  tunica  albuginea  and 
in  the  connective  tissue  between  the  convoluted  tubules.     They  con- 
verge toward  the  corpus 
Highmori      and      pass 
thence    to    the   spermatic 
cord. 

Retzius  (93)  and  Tim- 
ofeew  (94)  have  described 
plexuses  of  nonmedul- 
lated,  varicose  nerve-fibers 
surrounding  the  blood- 
vessels of  the  testis.  From 
such  plexuses  single 
fibers,  or  small  bundles  of 
such,  could  be  traced  to 
the  seminiferous  tubules, 
about  which  they  also 
form  plexuses.  Such 
fibers  have  not  been 
traced  into  the  epithelium 
lining  the  tubules.  In 
the  epididymis  Timofeew 
found  numerous  sympa- 
thetic ganglia,  the  cell- 
bodies  of  the  sympathetic 

neurones  of  which  were  surrounded  by  pericellular  plexuses.  In 
the  wall  of  the  vas  epididymidis  and  the  vasa  efferentia  were  observed 
numerous  varicose  nerve-fibers,  arranged  in  the  form  of  a  plexus, 
many  of  which  seemed  to  terminate  on  the  nonstriated  muscle  cells 
found  in  these  tubes.  Some  of  the  nerve-fibers  were  traced  into  the 
mucosa,  but  not  into  its  epithelial  lining. 


Fig.  279 — Section  of  dog's  testis  with  in- 
jected blood-vessels  (low  power)  :  a,  Seminifer- 
ous tubule ;  6,  connective-tissue  septum  ;  c,  blood- 
vessel. 


3.  THE  EXCRETORY  DUCTS. 

The  vas  defer  ens  possesses  a  relatively  thick  muscular  wall,  con- 
sisting of  three  layers,  of  which  the  middle  is  circular  and  the  other 
two  longitudinal.  The  subepithelial  mucosa  is  abundantly  supplied 
with  elastic  fibers  and  presents  longitudinal  folds.  The  lining  epi- 
thelium is  in  part  simple  ciliated  columnar  and  in  part  stratified 
ciliated  columnar,  with  two  rows  of  nuclei.  The  cilia  are,  however, 
often  absent,  beginning  with  the  lower  portion  of  the  vas  epidi- 


330 


THE    GENITOURINARY    ORGANS. 


dymidis.  According  to  Steiner,  the  epithelium  of  the  vas  deferens 
varies.  It  may  be  provided  with  cilia  in  the  lower  segments,  or  it 
may  even  be  similar  to  that  found  in  the  bladder  and  ureters. 

The  inner  muscular  layer  is  wanting  in  the  ampulla  of  the  vas 
deferens  ;  here  the  epithelium  is  mostly  simple  columnar  and  pig- 
mented.  Besides  the  folds,  there  are  also  evaginations  and  tubules 
which  sometimes  form  anastomoses — structures  which  may  be  re- 
garded as  glands. 

The  seminal  vesicles  are  also  lined,  at  least  when  in  a  distended 
condition,  by  simple,  nonciliated  columnar  epithelium  containing 
yellow  pigment.  In  a  collapsed  condition  the  epithelium  is  pseudo- 
stratified,  with  two  or  even  three  layers  of  nuclei.  The  arrange- 
ment of  the  epithelial  cells  in  a  single  layer  would  therefore  seem 
to  be  the  result  of  distention.  The  mucous  membrane  shows 


Epithelium. 


Mucosa. 


Inner  longi- 
tudinal 
muscular 
layer. 


-  Outer  lon- 
gitudinal 
muscular 
layer. 


Fig.  280. — Cross-section  of  vas  deferens  near  the  epididymis  (human). 

numerous  folds,  which,  in  the  guinea-pig  for  instance,  present  a 
delicate  axial  connective -tissue  stroma.  Besides  scanty  subepithe- 
lial  connective  tissue,  the  seminal  vesicles  are  provided  with  an  inner 
circular  and  an  outer  longitudinal  layer  of  muscle-fibers.  Sperma- 
tozoa are,  as  a  rule,  not  met  with  in  the  seminal  vesicles. 

The  epithelium  of  the  ejaculatory  ducts  is  composed  of  a  single 
layer  of  cells  ;  the  inner  circular  muscle-layer  is  very  poorly  devel- 
oped. In  the  prostatic  portion  of  the  ejaculatory  ducts  the  longi- 
tudinal muscle-layer  mingles  with  the  musculature  of  the  prostate 
and  loses  its  individuality.  The  ejaculatory  ducts  empty  either 
directly  into  the  urethra  at  the  colliculus  seminalis,  or  indirectly 
into  the  prostatic  portion  of  the  urethra  through  the  vesicula 
prostatica. 

The  prostate  is  a  compound  branched  alveolar  gland.    Its  capsule 


THE  MALE  GENITAL  ORGANS. 


331 


consists  of  dense  layers "  of  nonstriated  muscle-fibers,  connective 
tissue,  and  yellow  elastic  fibers.  Processes  and  lamellae  composed 
of  all  these  elements  extend  into  the  interior  of  the  gland,  converg- 
ing toward  the  base  of  the  colliculus  seminalis.  Between  the 
larger  trabeculae  are  situated  numerous  glands,  consisting  of  large, 


281. — Cross- section  of  wall  of  seminal  vesicle,  showing  the  folds  of  the 
mucosa  (human). 


Fig.  282. — From  section  of  prostate  gland  of  man. 

irregular  alveoli,  separated  by  fibromuscular  septa  and  trabeculae. 
The  alveoli  are  lined  by  simple  columnar  epithelium,  the  inner 
portion  of  the  cells  often  showing  aciclophile  granules.  Now  and 
then  the  alveoli  present  a  pseudostratified  epithelium,  with  two 
rows  of  nuclei  (Rudinger,  83).  A  basement  membrane,  although 


332  THE    GENITOURINARY    ORGANS. 

present,  is  difficult  to  demonstrate.  The  numerous  excretory  ducts, 
lined  by  simple  columnar  epithelium,  become  confluent  and  form 
from  15  to  30  collecting  ducts  which  empty,  as  a  rule,  either 
at  the  colliculus  seminalis  or  into  the  sulcus  prostaticus.  Near 
their  terminations  the  larger  ducts  are  lined  by  transitional  epithelium 
similar  to  that  lining  the  prostatic  portion  of  the  urethra. 

In  the  alveoli  of  the  glands,  peculiar  concentrically  laminated 
concrements  are  found,  known  as  prostatic  bodies  or  concretions 
(corpora  amylacea).  They  are  more  numerous  in  old  men,  but  are 
found  in  the  prostates  of  young  men  and  also  of  young  boys. 
The  secretion  of  the  prostate  (succus  prostaticus)  is  not  mucous 
in  character,  but  resembles  a  serous  secretion  and  has  an  acid  reac- 
tion. The  vesicula  prostatica  (sinus  pocularis)  is  lined  by  stratified 
epithelium,  consisting  of  two  layers  of  cells  and  provided  with  a  dis- 
tinct cuticular  margin  upon  which  rest  cilia.  In  its  urethral  region 
occur  short  alveolar  glands. 

The  glands  of  Cowper  are  branched  tubular  alveolar  glands, 
the  alveoli  being  lined  by  mucous  cells.  Crescents  of  Gianuzzi 
are,  however,  seldom  seen.  The  smaller  excretory  ducts,  lined  by 
cubical  epithelium,  unite  to  form  two  ducts,  one  on  each  side  of  the 
urethra ;  these  are  I  y2  inches  long,  and  are  lined  by  stratified  epi- 
thelium consisting  of  two  or  three  layers  of  cells. 

The  blood-vessels  of  the  prostate  ramify  in  the  fibromuscular 
trabeculae  and  form  capillary  networks  surrounding  the  alveoli.  The 
veins  collecting  the  blood  pass  to  the  periphery  of  the  gland,  where 
they  form  a  plexus  in  the  capsule.  The  lymphatics  begin  in  clefts 
in  the  trabeculae  and  follow  the  veins.  The  terminal  branches  of 
the  vessels  supplying  Cowper's  glands  are,  in  their  arrangement, 
like  those  of  other  mucous  glands. 

Numerous  sympathetic  ganglia  are  found  in  the  prostate  under 
the  capsule  and  in  the  larger  trabeculae  near  the  capsule.  The 
neuraxes  of  the  sympathetic  cells  of  these  ganglia  may  be  traced 
to  the  vessels  and  into  the  trabeculae  ;  their  mode  of  ending  has, 
however,  not  been  determined.  Small  medullated  nerve-fibers 
terminate  in  these  ganglia  in  pericellular  baskets.  Timofeew  has 
described  peculiar  encapsulated  sensory  nerve-endings,  found  in  the 
prostatic  and  membranous  portions  of  the  urethra  of  certain  mam- 
malia. They  consist  of  the  terminal  branches  of  two  kinds  of  nerves, 
inclosed  within  nucleated  laminated  capsules  :  one  large  medul- 
lated nerve -fiber,  after  losing  its  medullary  sheath,  breaks  up  into  a 
small  number  of  ribbon-shaped  branches  with  serrated  edges,  which 
may  pass  more  or  less  directly  to  the  end  of  the  nerve-ending  or 
may  be  bent  upon  themselves  ;  and  very  much  smaller  medullated 
nerve-fibers  which,  after  losing  their  medullary  sheaths,  divide  into 
a  large  number  of  varicose  fibers  which  form  a  dense  network  en- 
circling the  ribbon-shaped  fibers  previously  mentioned. 

The  penis  consists  of  three  cylindric  masses  of  erectile  tissue 
— the  two  corpora  cavernosa,  forming  the  greater  part  of  the  penis 


THE  MALE  GENITAL  ORGANS.  333 

and  lying  side  by  side,  and  the  corpus  spongiosum,  surrounding 
the  urethra  and  lying  below  and  between  the  corpora  cavernosa. 
The  two  latter  are  surrounded  by  a  dense  connective-tissue  sheath, 
the  tunica  albuginea.  These  erectile  bodies  are  surrounded  by  a 
thin  layer  of  skin,  containing  no  adipose  tissue  and  no  hair-follicles. 
The  corpus  spongiosum  is  enlarged  anteriorly  to  form  the  glans 
penis. 

The  principal  substance  of  the  erectile  bodies  is  the  so-called 
erectile  tissue :  septa  and  trabeculae,  consisting  of  connective 
tissue,  elastic  fibers,  and  smooth  muscle-cells  inclosing  a  sys- 
tem of  communicating  spaces.  These  latter  may  be  regarded  as 
venous  sinuses,  the  walls  of  which,  lined  by  endothelial  cells,  are 
in  apposition  to  the  erectile  tissue.  Under  certain  conditions  the 
venous  sinuses  are  distended  with  blood,  but  normally  they  are  in 
a  collapsed  state  and  form  fissures  which  simulate  the  clefts  found 
in  ordinary  connective  tissue.  In  other  words,  there  is  here  such 
an  arrangement  of  the  blood-vessels  within  the  erectile  tissue  that 
the  circulation  may  be  carried  on  with  or  without  the  aid  of  the 
cavernous  spaces.  The  arteries  of  the  corpora  cavernosa  possess 
an  especially  well-developed  musculature.  They  ramify  through- 
out the  trabeculae  and  septa  of  the  erectile  tissue  and  break  up 
within  the  septa  into  a  coarsely  meshed  plexus  of  capillaries.  A  few 
of  these  arteries  empty  directly  into  the  cavernous  spaces.  On  the 
other  hand,  the  arteries  give  off  a  rich  and  narrow-meshed  capillary 
network  immediately  beneath  the  tunica  albuginea.  This  is  in  com- 
munication with  a  deeper  and  denser  venous  network,  which,  in  turn, 
gradually  empties  into  the  venous  sinuses.  Aside  from  these  there 
are  anastomoses  between  the  arterial  and  venous  capillaries,  which 
later  communicate  with  the  venous  network  just  mentioned.  The 
blood  current,  regulated  as  it  thus  is,  may  pass  either  through 
the  capillaries  alone,  or  may  divide  and  flow  through  both  these 
and  the  venous  sinuses.  These  conditions  explain  both  the  erec- 
tile and  quiescent  state  of  the  penis.  The  relations  are  somewhat 
different  in  the  corpus  spongiosum  urethrae  and  in  the  glans  penis. 

The  epithelium  of  the  urethra  varies  in  the  several  regions.  The 
prostatic  portion  possesses  an  epithelium  similar  to  that  of  the 
bladder.  In  the  membranous  portion,  the  epithelium  may  be  simi- 
lar to  that  found  in  the  prostatic  portion,  but  more  often  pre- 
sents the  appearance  of  a  pseudostratified  epithelium  with  two  or 
three  layers  of  nuclei.  The  cavernous  region  is  lined  by  pseudo- 
stratified epithelium,  except  in  the  fossa  navicularis,  where  a 
stratified  squamous  epithelium  is  found.  Between  the  fibre-elastic 
mucosa  and  the  epithelium  there  is  a  basement  membrane.  There 
occur  in  the  urethra,  beginning  with  the  membranous  portion,  ir- 
regularly scattered  epithelial  sacculations  of  different  shapes.  Some 
of  these  show  alveolar  branching,  and  are  then  known  as  the  glands 
of  Littre. 

The  submucosa  of  the  cavernous  portion  of  the  urethra,  which 


334  THE    GENITO-URINARY    ORGANS. 

contains  nonstriated  muscle-tissue  arranged  circularly,  is  richly  sup- 
plied with  veins,  and  contains  pronounced  plexuses  communicating 
with  cavernous  sinuses,  which  correspond  in  general  to  those  of  the 
corpora  cavernosa  penis. 

In  the  glans  penis  the  cavernous  spaces  are  small  and  of  more 
regular  shape  than  in  the  corpora  cavernosa.  The  glans  is  covered 
by  a  layer  of  stratified  squamous  epithelium,  often  possessing  a  thin 
stratum  corneum  (see  Skin). 

Near  the  corona  of  the  glans  penis  there  are  now  and  then  found 
small  sebaceous  glands  (see  Hair),  known  as  glands  of  Tyson. 
The  prepuce  is  a  duplication  of  the  skin,  the  inner  surface  present- 
ing the  appearance  of  a  mucous  membrane. 

The  nerves  terminating  in  the  glans  penis  have  recently  been 
studied  by  Dogiel,  who  made  use  of  the  methylene-blue  method  in 
his  investigation.  He  finds  Meissner's  corpuscles  in  the  connective- 
tissue  papillae  under  the  epithelium,  Krause's  spheric  end-bulbs 
somewhat  deeper  in  the  connective  tissue,  and  the  genital  corpuscles 
situated  still  deeper  (see  Sensory  Nerve-endings).  In  the  epithelium 
are  found  free  sensory  nerve-endings.  Pacinian  corpuscles  have 
also  been  found  in  this  region. 


4.  SPERMATOGENESIS. 

In  order  that  the  student  may  obtain  an  understanding  of  the  com- 
plicated process  of  spermatogenesis  we  shall  give  a  description  of  it 
as  it  occurs  in  salamandra  maculosa,  which  of  all  vertebrate  animals 
presents  the  phenomena  in  their  simplest  and  best  known  form. 
The  student  should  understand,  however,  that  many  of  the  details 
here  described  have  not  been  observed  in  the  testes  of  mammalia ; 
and,  since  the  spermatozoa  of  many  of  the  mammalia  are  of  simpler 
structure  than  those  of  the  salamander,  the  development  of  the 
spermatozoa  of  the  former  is  consequently  simpler.  It  should  also 
be  noticed  that  the  general  structure  of  the  testes  of  the  salamander 
differs  in  some  respects  from  that  of  the  testes  of  mammalia,  as  given 
in  the  preceding  pages. 

At  first  the  seminiferous  tubules  consist  of  solid  cellular  cords, 
and  it  is  only  during  active  production  of  spermatozoa  that  a  central 
lumen  is  formed,  in  which  the  spermatosomes  then  lie.  The  cells 
which  compose  these  solid  cords  may  be  early  differentiated  into  two 
classes — those  of  the  one  class  being  directly  concerned  in  the  pro- 
duction of  the  spermatosomes  ;  those  of  the  other  appearing  to  have 
a  more  passive  role.  The  cells  of  the  first  class — the  spermatogo- 
nia,  or  primitive  seminal  cells — undergo  a  process  of  division  accom- 
panied by  an  increase  in  size.  In  this  way  they  soon  commence  to 
press  upon  the  cells  of  the  second  class — the  fotticutar  or  sustentacu- 
lar  cells.  The  result  is  that  the  nuclei  of  the  latter  are  forced  more 
or  less  toward  the  wall  of  the  seminal  tubule,  while  their  proto- 
plasm is  so  indented  by  the  adjacent  spermatogonia  that  the  cells 


SPERMATOGENESIS.  335 

assume  a  flattened  cylindric  shape  presenting  indentations  and 
processes  on  all  sides.  In  this  stage  the  spermatogonia  have  a 
radiate  arrangement  and  entirely  surround  the  elongated  susten- 
tacular  cells.  At  present  three  periods  are  distinguished  in  the 
development  of  the  male  sexual  cells  (spermatosomes)  from  the 
spermatogonia.  The  first  period  embraces  a  repeated  mitotic  divi- 
sion of  the  spermatogonia — the  period  of  proliferation.  In  the  sec- 
ond, the  spermatogonia,  which  have  naturally  become  smaller  from 
repeated  division,  begin  to  increase  in  size — the  period  of  growth. 
The  third  is  characterized  by  a  modified  double  mitotic  division 
without  intervening  period  of  rest,  and  results  in  the  matured  sper- 
matozoa— the  period  of  maturation,  figure  283.  During  the  third 
period,  a  very  important  and  significant  process  takes  place — the 

Primordial  sexual  cell. 


/Zone  of  proliferation. 
(The  generations  are 
much  larger.) 


Zone  of  growth. 

/ 

Spermatocyte  I  order.- 

Spermatocytes  II  order.—         — •  •  ' Zone  of  maturation. 

Spermatids. 

Fig.  283. — Schematic  diagram  of  spermatogenesis  as  it  occurs  in  ascaris  (after  Boveri). 
("Ergebn.  d.  Anat.  u.  Entw.,"  Bd.  I.) 

reduction  in  the  number  of  chromosomes,  so  that  in  the  spermatids, 
the  chromosomes  are  reduced  to  half  the  number  present  in  a 
somatic  cell  of  the  same  animal.  The  manner  in  which  this  reduc- 
tion in  the  number  of  chromosomes  takes  place  will  be  described  as 
it  occurs  in  salamandra  maculosa. 

After  the  cells  composing  the  last  generation  of  spermato- 
gonia have  attained  a  certain  size  (period  of  growth),  they  under- 
go karyokinetic  division.  First,  the  usual  skein  or  spirem  is 
formed,  but  instead  of  dividing  into  twenty-four  chromosomes,  as 
in  the  somatic  cell,  the  filament  of  the  skein  segments  into  only 
twelve  loops.  The  cell  thus  provided  with  twelve  chromosomes 
now  enters  upon  the  period  of  maturation,  and  is  known  as  a 
spermatocyte  of  the  first  order,  or  a  "  mother  cell  "  (O.  Hert- 


336  THE    GENITOURINARY    ORGANS. 

wig,  90).  The  division  of  these  cells  is  heterotypic  (ind.  p.  64) ; 
the  chromosomes  split  longitudinally  and  in  such  a  way  that  the 
division  begins  at  the  crown  of  the  loops,  extending  gradually 
toward  their  free  ends.  In  this  case  the  daughter  chromosomes 
remain  for  some  time  in  contact,  so  that  the  metakinetic  figure 
resembles  a  barrel  in  shape.  Finally,  the  daughter  chromosomes 
separate  and  wander  toward  the  poles.  As  soon  as  the  daughter 
stars  (diaster)  are  developed,  the  number  of  chromosomes  is  again 
doubled  by  a  process  of  longitudinal  division.  The  spermatocyte 
of  the  first  order  thus  divides  into  two  spermatocytes  of  the  second 
order,  or  daughter  cells  (O.  Hertwig,  90).  The  nuclei  of  the 
daughter  cells  now  contain  twenty-four  chromosomes,  as  is  the 
case  in  the  somatic  cell,  and,  without  undergoing  longitudinal  split- 
ting, the  daughter  chromosomes  are  distributed  to  the  two  nuclei 
of  the  spermatids.  In  other  words,  the  latter  contain  only  twelve 
chromosomes.  The  spermatozoa  are  formed  from  the  spermatids 
by  a  rearrangement  of  the  constituent  elements  of  these  cells.  It 
may  thus  be  said  that  even  in  the  stage  of  the  segmenting  skein  in 
the  mother  cells,  the  spermatocytes  of  the  first  degree  contain  twice 
as  many  chromosomes  as  a  somatic  cell,  a  condition  which  is 
first  clearly  seen  in  the  stage  of  the  diaster  (here  only  an  apparent 
duplication  in  the  diaster  stage).  As  a  result,  there  is,  first,  a  de- 
crease in  the  double  number  of  chromosomes  found  in  the  sperma- 
tocytes of  the  second  degree  to  the  normal  number ;  second,  a 
decrease  in  the  number  of  chromosomes  in  the  spermatocytes  of  the 
third  degree  (spermatids)  to  one-half  the  number  present  in  a 
somatic  cell,  a  condition  probably  due  to  the  fact  that  here  there 
is  no  stage  of  rest  nor  longitudinal  splitting  of  the  chromosomes. 
This  is  the  general  process  in  heterotypic  division.  Besides  the 
heterotypic  form,  there  occurs  in  the  division  of  the  spermatocytes 
another  (homeotypic)  form  of  karyokinetic  cell-division.  This  dif- 
fers from  the  heterotypic  in  the  shortness  of  the  chromosomes,  the 
absence  of  the  barrel  phase,  the  late  disappearance  of  the  aster, 
and  the  absence  of  duplication  in  the  chromosomes  of  the  diaster. 
According  to  Meves  (96),  the  spermatocytes  of  the  first  degree 
undergo  heterotypic,  those  of  the  second  degree,  homeotypic 
division. 

The  spermatids  develop  into  the  spermatozoa,  beginning  imme- 
diately after  the  close  of  the  second  division  of  maturation.  This 
process  has  been  fully  described  for  salamandra  maculosa  by  Her- 
mann, Flemming,  Benda,  and  others,  but  need  not  engage  our 
attention  at  this  point  beyond  the  statement  that  the  chromatin  of 
the  nuclei  of  the  spermatids  develops  into  the  heads  of  the  sperma- 
tozoa, while  the  remaining  structures  are  developed  from  the  proto- 
plasm. "  The  mature  spermatozoon  of  the  salamander  represents 
a  completely  metamorphosed  cell  ;  in  the  course  of  its  develop- 
ment no  portion  of  the  original  cell  is  cast  off"  (Meves,  97). 

Spermatogenesis  in  mammalia  may  be  compared  to  the  foregoing 


SPERMATOGENESIS. 


337 


process,  with  the  exception  that  here  the  different  stages  are  seen 
side  by  side  in  the  seminiferous  tubule  and  without  any  apparent 
sequence,  making  the  successive  stages  more  difficult  to  demon- 
strate. The  various  generations  of  cells  form  columns,  and  are 
arranged  in  such  a  manner  that  the  younger  are  found  near  the 
lumen  and  the  older  close  to  the  wall  of  the  tubule.  (Figs.  284  and 


9 


Fig.  284. — Schematic  diagram  of  section  through  convoluted  seminiferous  tubule 
of  mammal,  showing  the  development  of  the  spermatosomes.  The  number  of  chromo- 
somes is  not  shown  in  the  various  generations  of  the  spermatogenic  cells.  The  pro- 
gressive development  of  the  spermatogenic  elements  is  illustrated  in  the  eight  sectors 
of  the  circle  :  a,  Young  sustentacular  cell  ;  b,  spermatogonium  ;  c,  spermatocyte  ;  dt 
spermatid.  Iri  I,  2,  3,  and  4  the  spermatids  rest  on  the  enlarged  sustentacular  cell  in  the 
center  of  the  sector  ;  on  both  sides  of  the  sustentacular  cells  are  the  spermatogenic  or 
mother  cells  in  mitosis.  In  the  sectors  5>  6,  7,  and  8  spermatozoa  are  seen  in  ad- 
vanced stages  resting  on  the  sustentacular  cells,  with  new  generations  of  spermatids  on 
each  side.  [From  Rauber  (after  Brown)  with  changes  (after  Hermann).] 


285.)  These  columns  are  separated  from  each  other  by  high  sus- 
tentacular cells,  or  Sertoli's  cells  or  columns.  The  metamorphosis 
of  the  cells  into  spermatids  and  spermatosomes  is  accomplished 
by  the  changing  of  the  cells  bordering  upon  the  lumen  and  then 
of  those  in  the  deeper  layers,  etc.,  into  spermatids  and  then 
into  spermatosomes.  During  this  process  the  spermatids  arrange 

22 


338 


THE    GENITOURINARY    ORGANS. 


themselves  around  the  ends  of  Sertoli's  columns,  a  phenomenon 
which  was  formerly  regarded  as  representing  a  copulation  of  the 
two  elements,  although  it  was  clearly  understood  that  no  real 
fusion  or  interchange  of  chromatin  occurred,  but  that  the  close 
relations  of  the  two  were  for  the  purpose  of  furnishing  nourishment 
to  the  developing  spermatosomes.  The  whole  forms  a  spermato- 
blast  of  von  Ebner.  Since  the  spermatids  lining  the  lumen  are 
changed  into  spermatozoa,  and  the  process  is  repeated  in  the  cells 
of  the  deeper  layers  as  they  come  to  the  surface,  the  result  is  that 
the  entire  column  is  finally  used  up.  The  compensatory  elements 
are  supplied  by  the  proliferation  of  the  adjacent  spermatogonia. 
The  resulting  products  again  divide,  and  thus  build  up  an  entirely 
new  generation  of  spermatogenic  cells.  Hand  in  hand  with  these 
progressive  phenomena  occurs  an  extensive  destruction  of  the  cells 
taking  part  in  spermatogenesis.  This  is  shown  by  the  presence  of 
so-called  karyolytic  figures  in  the  cells,  which  later  suffer  complete 
demolition. 

These  developmental   changes   are  represented  in  the  preced- 


isl|t|^^ 


Fig.  285. — Section  of  convoluted  tubule  from  rat's  testicle  (after  von  Ebner, 
88).  The  pyramidal  structures  are  the  sustentacular  cells,  together  with  spermatids  and 
spermatosomes.  Between  these  are  spermatogenic  cells,  some  of  which  are  in  process 
of  mitotic  division.  Below,  on  the  basement  membrane  and  concealing  the  spermato- 
gonia, are  black  points  representing  fat-globules,  a  characteristic  of  the  rat's  testicle. 
Fixation  with  Flemming'  s  fluid. 

ing  schematic  figure  (Fig.   284),  and  may  in  part  be  observed  in 
figure  285. 

In  mammalia  it  has  been  possible  to  trace  the  development 
of  the  spermatids  into  the  spermatosomes.  These  phenomena  have 
been  studied  and  described  by  numerous  writers,  and  although 
many  conflicting  views  have  been  expressed,  the  essential  steps  of 
this  process  seem  quite  clearly  established.  The  account  here 
given  is  based  in  part  on  the  recent  observations  of  v.  Lenhossek 
and  the  observations  of  Benda.  Before  considering  the  method  of 
development  of  the  spermatosomes  from  the  spermatids,  a  few  words 
concerning  the  structure  of  the  latter  may  be  useful.  The  sharply 
outlined  spermatid  possesses  a  slightly  granular  protoplasm  and  a 
round  or  slightly  oval  nucleus  with  a  delicate  chromatic  network. 
In  the  protoplasm  there  is  found  a  sharply  defined  globule,  known 
as  the  sphere  or  sphere  substance,  which  lies  near  the  nucleus  and 


SPERM  ATOGENESIS.  339 

presents  throughout  a  nearly  homogeneous  structure.  This  sub- 
stance is  first  noticed  in  the  spermatocytes,  disappears  during  the 
cell-divisions  resulting  in  the  spermatids,  and  reappears  in  the  latter. 
In  the  protoplasm  of  the  spermatid,  lying  near  the  nucleus,  there 
is  further  found  a  small  globular  body,  the  chromatoid  accessory 
nucleus  of  Benda,  smaller  than  the  sphere  and  staining  very  deeply 
in  Heidenhain's  hematoxylin.  A  true  centrosome  may  also  be 
found  in  the  spermatid. 

The  nucleus  of  the  spermatid  develops  into  the  head  of  the 
spermatosome,  during  which  change  the  originally  spheric  nucleus 
becomes  somewhat  flattened  and  at  the  same  time  assumes  a  denser 
structure  and  moves  toward  that  portion  of  the  spermatid  pointing 
away  from  the  lumen  of  the  seminiferous  tubule.  Accompanying 
these  changes  in  the  nucleus,  marked  changes  are  observed  in  the 
shape  and  structure  of  the  sphere,  which  marks  the  position  of  the 
future  anterior  end  of  the  head  of  the  spermatosome,  and  applies 
itself  to  the  nucleus  on  the  side  pointing  away  from  the  lumen  of 
the  tubule.  In  this  position  it  differentiates  into  an  outer  clear 
homogeneous  zone  and  a  central  portion  which  stains  more  deeply 
and  to  which  v.  Lenhossek  has  given  the  name  akrosome.  From 
these  structures  are  developed  the  head-cap  and  the  lance  of  the 
spermatosomes,  which  differ  in  shape  and  relative  size  in  the  sper- 
matosomes  of  the  different  vertebrates.  Recent  investigation  seems 
to  establish  quite  clearly  that  the  axial  thread  of  the  tail  is  devel- 
oped from  the  centrosome  (from  the  larger,  if  two  are  present),  which 
is  situated  at  some  distance  from  the  nucleus.  Soon  after  the  begin- 
ning of  the  development  of  the  axial  thread  the  centrosome  wanders 
to  the  posterior  part  of  the  future  head  of  the  spermatosome  (the 
pole  of  the  nucleus  opposite  the  head-cap)  and  becomes  firmly 
attached  to  the  nuclear  membrane  in  this  position  (observations 
made  on  the  rat  by  v.  Lenhossek,  and  on  the  salamander  by  Meves). 
The  middle  piece  and  the  undulating  membrane,  it  would  appear, 
are  differentiated  from  the  protoplasm,  although  the  question  of  the 
mode  of  their  development  is  still  open  to  discussion.  The  chro- 
matoid body  assumes  a  position  near  the  axial  thread  at  its  junc- 
tion with  the  cell  membrane ;  its  fate  has  not,  however,  been  fully 
determined. 

According  to  Hermann  (97),  the  end-piece  in  the  selachia  is 
derived  from  the  centrosome,  the  ring-shaped  body  from  the  invagi- 
nated  half  of  the  intermediate  body  of  the  spermatid  formed  during 
the  last  spermatocytic  division,  and  the  axial  thread  from  filaments  of 
the  proximal  half  of  the  central  spindle.  The  lance,  according  to 
him,  represents  a  modified  portion  of  the  nuclear  membrane  of  the 
spermatid. 

For  further  particulars  regarding  spermatogenesis  see  the  in- 
vestigations of  v.  la  Valette  St.  George,  67-87  ;  v.  Brunn,  84 ; 
Biondi,  Benda,  Meves,  and  v.  Lenhossek. 


34O  THE    GENITOURINARY    ORGANS. 

TECHNIC 

278.  The  ovaries  of  the  smaller  animals  are  better  adapted  to  study 
than  those  of  the  human  being,  since  the  former  are  more  easily  fixed. 

279.  The  germinal  epithelium  and  its  relations  to  the  egg-tubes  of 
Pfliiger  are  best  studied  in  the  ovaries  of  young  or  newly  born  animals — 
cats,  for  instance,  being  especially  well  adapted  to  this  purpose. 

280.  Normal  human  ovaries  are  usually  not  easily  obtainable.     Human 
ovaries  very  often  show  pathologic  changes,  and  in  middle  life  frequently 
contain  but  few  follicles. 

281.  Fresh  ova  may  be  easily  procured  from  the  ovaries  of  sheep,  pig, 
or  cow  in  the  slaughter-houses.      On  their  surfaces  are  prominent  trans- 
parent areas — the  larger  follicles.     If  a  needle  be  inserted  into  one  of 
these  follicles  and  the  liquor  folliculi  be  caught  upon  a  slide,  the  ovum 
may  as  a  rule  be  found,  together  with  its  corona  radiata.     That  part  of 
the  preparation  containing  the  ovum  should  be  covered  with  a  cover-glass 
under  the  edges  of  which  strips  of  cardboard  are  laid.      If  no  such  strips 
are  employed,  the  zona  pellucida  of  the  ovum  is  likely  to  burst  in  the  field 
of  vision,  giving  rise  to  a  funnel-shaped  tear.     These  tears  have  often 
been  pictured  and  described  as  preformed  canals  (micropyles). 

282.  The  best  fixing  fluid  for  ovarian  tissue  is  Flemming's  or  Her- 
mann's (vid.  T.  17,   18),  either  of  which  may  be  used  for  small  ovaries 
or  pieces  of  large  ovaries  ;  safranin  is  then  used  for  staining.     Good  results 
are  also  obtained  with  corrosive  sublimate  (staining  with  hematoxylin 
according  to  M.  Heidenhain),  and  also  with  picric  acid  (staining  with 
borax -carmin). 

283.  The  treatment  of  the  Fallopian  tubes  is  the  same  as  that  of  the 
intestine  ;  in  order  to  obtain  cross-sections  of  a  tube  it  is  advisable  to  dis- 
sect away  the  peritoneum  near  its  line  of  attachment  and  then  distend  the 
tube  before  fixing.     It  is  instructive  to  dilate  the  tube  by  filling  it  with 
the  fixing  agent,  thus  causing  many  of  the  folds  to  disappear. 

284.  No  special  technic  is  necessary  in  fixing  the  uterus  and  vagina. 
The  epithelium  is,  however,  best  isolated  with  one-third  alcohol  (vid. 
T.  128). 

285.  Seminal  fluid  to  which  normal  salt  solution  has  been  added  may 
be  examined  in  a  fresh  condition.     The  effect  upon  the  spermatozoa  of  a 
very  dilute  solution  of  potassium  hydrate  ( i  %  or  weaker)  or  of  a  very 
dilute  acid  (acetic  acid)   is  worth  noticing.     The  spermatozoa  of  sala- 
mandra  maculosa  show  the  different  structural  parts  very  clearly  (lance, 
undulating  membrane,  marginal  thread,   etc.).     In  macerated  prepara- 
tions (very  dilute  chromic  acid),  or  in  those  left   for  some  time  in  a 
moist  chamber,  the  fibrillar  structure  of  the  marginal  and  axial  threads 
may  be  seen  quite  distinctly.     The  spermatozoa  may  also  be  examined 
in  the  form  of  dry  preparations  (treatment  as  for  blood),  stained,  for 
instance,  with  safranin.     Osmic  acid,  its  mixtures,  and  osmic  vapors  are 
useful  as  fixing  agents,  certain  structures  being  better  brought  out  so  than 
by  employing  the  dry  methods. 

286.  In  examining  the  testicle  (spermatogenesis)  it  is  advisable  to 
begin  with  the  testis  of  the  salamander,  which  does  not  show  such  com- 
plicated structures  as  do  the  testes  of  mammalia.      Here  also  either  Flem-  • 
ming's  or  Hermann's  fluid  maybe  used  as  a  fixing  agent,  the  latter  being 


THE    SKIN.  341 

followed  by  treatment  with  crude  pyroligneous  acid  (vid.  T.  18).  For 
the  salamander  Hermann  recommends  a  mixture  composed  of  i  %  plati- 
num chlorid  15  c.c.,  2%  osmic  acid  2  c.c.,  and  glacial  acetic  acid  i  c.c., 
and  for  mammalia  the  same  solution  with  double  the  amount  of  osmic  acid. 
This  fluid  is  allowed  to  act  for  some  days,  the  specimen  then  being 
washed  for  twenty-four  hours  in  running  water  and  carried  over  into  alco- 
hols of  ascending  strengths.  Paraffin  sections  are  treated  as  follows  :  Place 
for  from  twenty-four  to  forty-eight  hours  in  safranin  (safranin  i  gm.  is 
dissolved  in  10  c.c.  of  absolute  alcohol  and  diluted  with  90  c.c.  of  anilin 
water;  vid.  T.  119).  After  decolorizing  with  pure  or  acidulated  absolute 
alcohol  the  sections  are  placed  for  three  or  four  hours  in  gentian -violet 
(saturated  alcoholic  solution  of  gentian -violet  5  c.c.  and  anilin  water 
100  c.c. ),  and  are  then  placed  fora  few  hours  in  iodo-iodid  of  potassium 
solution  until  they  have  become  entirely  black  (iodin  i,  iodid  of  potas- 
sium 2,  water  300);  finally,  they  are  washed  in  absolute  alcohol,  until 
they  become  violet  with  a  dash  of  brown.  The  various  structures  appear 
differently  stained  :  for  instance,  the  chromatin  of  the  resting  nucleus 
and  of  the  dispirem,  bluish-violet ;  the  true  nucleoli,  red ;  while,  on  the 
other  hand,  in  the  aster  and  diaster  stages  the  chromatin  stains  red. 

It  is  of  especial  importance  that  small  testicles  should  not  be  cut  into 
pieces  before  fixing,  as  this  causes  the  seminal  tubules  to  swell  up  and 
show  marked  changes,  even  in  regions  at  some  distance  from  the  cut 
(Hermann,  93,  I). 

The  treatment  of  the  remaining  parts  of  the  male  reproductive  organs 
requires  no  special  technic. 


VI.  THE  SKIN  AND  ITS  APPENDAGES. 

A.  THE  SKIN  (CUTIS). 

THE  skin  consists  of  two  intimately  connected  structures — the 
one,  of  mesodermic  origin,  is  the  true  skin,  corium  or  dermis  ;  the 
other,  of  ectodermic  origin,  is  the  epidermis  or  cuticle.  The  super- 
ficial layer  of  the  corium  is  raised  into  ridges  and  papillae  which 
penetrate  into  the  epidermis,  the  spaces  between  the  papillae  being 
filled  with  epidermal  elements.  Thus,  the  lower  surface  of  the 
epidermis  is  alternately  indented  and  raised  into  a  system  of  furrows 
and  elevations  corresponding  to  the  molding  of  the  corium. 

In  the  epidermis  two  layers  of  cells  may  be  observed — the 
stratum  Malpighii,  or  stratum  germinativum  (Flemming),  and  the 
horny  layer,  or  stratum  corneum.  According  to  the  shape  and 
characteristics  of  its  cells,  the  stratum  germinativum  may  also  be 
divided  into  three  layers — first,  the  deep  or  basal  layer,  consisting 
of  columnar  cells  resting  immediately  upon  the  corium  ;  second, 
the  middle  layer,  consisting  of  polygonal  cells  arranged  in  several 
strata,  the  number  of  the  latter  varying  according  to  the  region  of 
the  body ;  and  third,  the  upper  layer,  or  stratum  gramilosnm, 
which  is  composed,  at  most,  of  two  or  three  strata  of  gradually 
flattening  cells  characterized  by  their  peculiar  granular  contents. 


342 


THE    SKIN   AND    ITS    APPENDAGES. 


All  these  cell  layers  consist  of  prickle  cells,  and  for  this  reason  the 
stratum  Malpighii  is  sometimes  known  as  the  stratum  spinosum. 
When  these  cells  are  isolated  by  certain  methods,  their  surfaces  are 
seen  to  be  provided  with  short,  thread-like  processes.  In  section 
the  cells  appear  to  be  joined  together  by  their  processes.  Since  it 
has  been  proved  that  the  processes  of  adjacent  cells  do  not  lie  side 
by  side,  but  meet  and  fuse,  they  must  be  regarded  as  belonging  alike 
to  both  cells.  Between  the  fused  processes,  which  are  known  as 
intercellular  bridges,  there  exists  a  system  of  channels  which  is  in 
communication  with  the  lymphatic  system  of  the  corium.  The 
prickles  just  mentioned  are  variously  regarded  by  different  investi- 
gators ;  some  considering  them  to  be  exclusively  protoplasmic 


Fig.  286. — Under  surface  of  the  epidermis,  separated  from  the  cutis  by  boiling.  The 
sweat-glands  may  be  traced  for  a  considerable  part  of  their  length ;  X  4°  :  tf>  Sweat- 
gland  ;  b,  longitudinal  ridge  ;  <-,  depression ;  d,  cross-ridge. 

processes  of  the  cells,  others  regarding  them  as  derived  from  the 
membranes  of  the  cells  composing  the  stratum  Malpighii.  Ranvier 
and  others  ascribe  a  fibrillar  structure  to  the  peripheral  portion  of 
the  cellular  protoplasm,  and,  according  to  them,  these  nbrillae, 
surrounded  by  a  small  quantity  of  indifferent  protoplasm,  form 
the  processes.  Ranvier  has  also  shown  that  such  fibrillae  may 
extend  from  one  cell  around  several  others  before  reaching  their 
ultimate  destination  in  other  cells  at  some  distance.  (Fig.  288.)  The 
cells  of  the  stratum  granulosum  contain  peculiar  deposits  of  a  sub- 
stance to  which  Waldeyer  has  given  the  name  of  keratohyalin. 
This  substance  occurs  in  the  form  of  irregular  bodies  varying  in  size 
and  imbedded  in  the  protoplasm.  The  nuclei  of  such  cells  always 


THE    SKIN. 


343 


show  degenerative  processes,  which  are  possibly  due  to  the  forma- 
tion of  the  keratohyalin  (Mertsching,  Tettenhamer).  These  karyo- 
lytic  figures  and  keratohyalin  possess  in  common  many  apparently 
identical  microchemic  peculiarities,  and  it  is  very  probable  that 
karyolysis  and  the  formation  of  keratohyalin  are  processes  origin- 
ally very  closely  allied — i.  e.,  that  the  keratohyalin  is  derived  from 
the  fragments  of  the  dying  nucleus. 

The  stratum  corneum  forms  the  outer  layer  of  the  epidermis  and 
presents,  as  a  rule,  a  somewhat  differentiated  lower  stratum.     This 


Stratum  corneum. 


Duct  of  sweat- 
gland. 

Corium. 


V.  . 


Stratum  Malpighii. 


Subcutis. « 


-""Blood-vessel. 
K— -Sweat-gland. 


Fig.  287. — Cross-section  of  skin  of  child,  with  blood-vessels  injected  ;  X  3°- 

latter  is  more  especially  noticeable  in  those  regions  in  which  the 
stratum  corneum  is  highly  developed,  and  is  known  as  the  stratum 
luciduin.  It  is  quite  transparent,  this  property  being  due  to  the 
presence  in  its  cells  of  a  homogeneous  substance,  the  eleidin. 
Eleidin  is  in  all  probability  a  derivative  of  the  more  solid  keratohy- 
alin of  the  stratum  granulosum.  The  cells  of  the  stratum  corneum 
are  more  or  less  flattened  and  cornified,  especially  at  their  periphery. 
This  applies  more  particularly  to  the  superficial  cells.  In  the  inte- 
rior of  each  cell  a  more  or  less  degenerated  nucleus  may  be  seen, 
but  otherwise  its  contents  are  homogeneous,  or,  at  most,  arranged 


344 


THE    SKIN   AND    ITS    APPENDAGES. 


in  concentric  lamellae  (Kolliker,  89).  Here  and  there  between  the 
cornified  cells  structures  may  be  seen  which  probably  represent  the 
remains  of  intercellular  bridges.  The  thickness  of  the  epidermis 
varies  greatly  according  to  the  locality,  and  is  directly  proportionate 
to  the  number  of  its  cell  layers.  As  a  rule,  the  stratum  Malpighii 
is  thicker  than  the  stratum  corneum,  but  in  the  palm  of  the  hand 
and  the  sole  of  the  foot  the  latter  is  considerably  the  thicker. 

The  various  layers  of  the  epidermis  are  in  close  genetic  relation- 
ship to  one  another.  The  constant  loss  to  which  the  epidermis  is 
subjected  by  desquamation  is  compensated  by  a  continuous  upward 
pushing  of  its  lower  elements  ;  cell-proliferation  occurs  in  the 
basal  cells  and  adjacent  cellular  strata  of  the  stratum  germinativum 
(Malpighii),  where  the  elements  are  often  seen  in  process  of  mitotic 
division.  The  young  cells  are  gradually  pushed  outward,  and  dur- 
ing their  course  assume  the  general  characteristics  of  the  elements 

composing  the  layers 
through  which  theypass. 
For  instance,  such  a  cell 
changes  first  into  a  cell 
of  the  stratum  germina- 
tivum ;  then,  when  it 
commences  the  forma- 
tion of  keratohyalin,  into 
a  cell  of  the  stratum 
granulosum  ;  later,  into 
a  cell  of  the  stratum  lu- 
cidum,  and  finally  into 
an  element  of  the  stra- 
tum corneum,  where  it 
loses  its  nucleus,  corni- 
fies,  and  at  last  drops  off. 
The  mesodermic  por- 
tion of  the  skin,  the  co- 
rium, consists  of  a  loose, 

subcutaneous  connective  tissue  containing  fat,  the  subcutaneous 
layer,  with  the  panniculus  adiposus,  and  of  the  true  skin,  or 
corium  proper.  The  amount  of  adipose  tissue  in  the  subcutaneous 
layer  is  subject  to  great  variation  ;  there  are,  however,  a  few  re- 
gions in  which  there  is  normally  very  little  or  no  fat  (external  ear, 
eyelids,  scrotum,  etc.).  To  the  subcutaneous  connective  tissue  is 
due  the  mobility  of  the  skin.  The  corium  may  be  compared  to  the 
mucosa  of  a  mucous  membrane,  and  consists  of  two  layers — of  a 
deeper  and  looser  pars  reticularis,  and  of  a  superficial  pars  papillaris 
supporting  the  papillae.  The  transition  from  the  one  to  the  other 
is  very  gradual.  Elastic  fibers  are  present  in  the  connective  tissue 
of  both  layers. 

The  pars  reticularis  is  made  of  bundles  of  connective-tissue  fibers 
arranged  in  a  network,  nearly  all  of  the  strands  of  which  have  a  direc- 


Fibrils  which 
pass  from  one 
cell  to  another. 


Nucleolus.    -- 


Intercellular 
bridges. 


Nucleus  of 
cell. 


Fig.  288. — Prickle  cells  from  the  stratum  Malpighii 
of  man  ;  X  4^°- 


THE    SKIN. 


345 


tion  parallel  with  the  surface  of  the  skin  and  are  surrounded  by  a  retic- 
ulum  of  rather  coarse  elastic  fibers.  In  that  portion  of  the  pars  papil- 
laris  bordering  upon  the  epidermis,  the  interlacing  strands  of  con- 
nective tissue,  as  well  as  the  surrounding  reticulum  of  elastic  fibers, 
are  finer,  so  that  the  whole  tissue  is  denser.  This  stratum  supports 
the  papillae — knob-like  or  conical  elevations  of  still  denser  tissue  end- 
ing in  one  or  more  points.  We  accordingly  speak  of  simple  or  com- 
pound papillae.  These  structures  are  especially  numerous  and  well 
developed  in  the  palm  of  the  hand  and  sole  of  the  foot,  where  they 
are  from  1 10  p.  to  220  /J.  long.  Here  they  rest  upon  ridges  of  the 
corium,  which  are  nearly  always  arranged  in  double  rows.  Accord- 
ing to  whether  the  papillae  contain  blood-vessels  alone,  or  special 
nerve-endings  also,  they  are  known  as  vascular  or  tactile  papillae. 


Stratum 
corneum. 


Lower  border  "~~ 
of    stratum 
lucidum. 
Stratum  granu- 
losum. 


Stratum  Mal- 
pighii. 


Fig.  289. — Cross-section  of  human  epidermis  ;  the  deeper  layers  of  the  stratum 
Malpighii  are  not  represented  ;  X  75°- 


The  smallest  papillae  are  found  in  the  mammse  and  scrotum — from 
30  /*  to  50  //  long.  The  surface  of  the  pars  papillaris  is  covered  by 
an  extremely  delicate  membrane — the  basement  membrane.  Accord- 
ing to  most  authors,  the  basal  cells  of  the  epidermis  are  simply 
cemented  to  this  structure.  Others  believe  that  the  epithelial  cells 
are  provided  with  short  basilar  processes  which  penetrate  into  the 
basement  membrane  and  meet  here  with  similar  structures  from  the 
connective-tissue  cells  of  the  corium.  This  would  give  the  base- 
ment membrane  a  fibrillar  structure  (Schuberg). 

The  subcutaneous  layer  contains  numerous  more  or  less  verti- 
cal strands  of  connective  tissue,  containing  numerous  large  elastic- 
tissue  fibers  and  joining  the  stratum  reticulare  of  the  corium  to  the 


346  THE    SKIN   AND    ITS    APPENDAGES. 

superficial  fascia  of  the  body  or  underlying  structure,  whatever  that 
may  be.  These  strands  are  the  retinaculce  cutis,  and  inclose  in 
their  meshes  masses  of  fatty  tissue  which  form  the  panniculus 
adiposus.  The  latter  varies  greatly  in  thickness  in  different  parts 
of  the  body.  The  vertically  arranged  cords  of  connective  tissue 
are  accompanied  by  blood-vessels,  nerves,  and  the  excretory  ducts 
of  glands. 

Smooth  muscle-fibers  are  also  present  in  the  skin,  and  around 
the  hair  follicles  are  grouped  into  bundles.  Nearly  continuous 
layers  of  smooth  muscle  tissue  are  found  in  the  subcutaneous  layer 
of  the  scrotum  (forming  here  the  tunica  dartos),  in  the  perineum, 
in  the  areolae  of  the  mammse,  etc.  In  the  face  and  neck  striated 
muscle-fibers  also  extend  outward  into  the  corium. 

Even  in  the  white  race  certain  regions  of  the  epidermis  always 
contain  pigment — as,  for  instance,  the  areolae  and  mammillae  of  the 


Stratum 
corneum. 


Pigment 

Y_        ,--**'*":-  -.«v^--~~     cell    with 

^v$*|         two     pro- 
-i^fjiP        cesses. 

Processof  ."„.-  ^~" '  Pigmented 

pigment 1^-;  basal  cell. 


Fig.  290. — Cross-section  of  negro's  skin,  showing  the  intimate  relationship  of  the 
pigment  cells  of  the  corium  to  the  basilar  cells  of  the  epidermis.  The  latter  are  more 
deeply  pigmented  at  their  outer  ends.  The  pigment  granules  may  be  traced  into  the 
outermost  layers  of  the  stratum  corneum  ;  X  525- 

mammary  glands,  the  scrotum,  labia  majora,  around  the  anus,  etc. 
In  these  regions  the  epithelial  cells  and  the  connective-tissue  cells  of 
the  pars  papillaris  corii  contain  a  variable  number  of  small  pigment 
granules.  The  latter  occur  chiefly  in  the  basal  cells  of  the  epider- 
mis and  diminish  perceptibly  in  the  cells  of  the  overlying  layers,  so 
that  in  those  of  the  stratum  corneum  few,  if  any,  are  left.  In 
negroes  and  other  colored  races  the  deep  pigmentation  is  due  to  a 
similar  distribution  of  the  pigment  granules  in  the  entire  epidermis  ; 
but  even  here  the  pigmentation  decreases  toward  the  surface, 
although  the  uppermost  cells  of  the  stratum  corneum  always  con- 
tain some  pigment.  The  nuclei  of  the  cells  are  always  free  from  the 
coloring-matter.  The  question  as  to  the  origin  of  the  pigment  is 
as  yet  unsolved.  This  much  is  known  :  that  in  those  regions  where 
pigment  is  present  certain  branched  and  deeply  pigmented  connec- 


THE    SKIN.  347 

tive-tissue  cells  are  found  immediately  beneath  the  epidermis,  sending 
out  processes  which  may  be  traced  outward  between  the  cells  of 
the  stratum  Malpighii  (Aeby).  This  fact  has  led  some  authors  to 
believe  that  the  connective  tissue  is  in  reality  the  source  of  the  pig- 
ment, and  that  by  some  unknown  process  the  latter  is  taken  up  and 
conveyed  to  the  cells  of  the  epidermis.  This  theory  would  preclude 
a  direct  production  of  pigment  granules  in  the  epidermal  cells.  But 
although  it  can  not  be  denied  that  the  pigment  may  be  derived  from 
the  connective  tissue,  it  is  hardly  logical  to  assume  a  priori  that 
epithelial  cells  are  not  capable  of  pigment  production,  since,  in  other 
regions  of  the  body,  pigment  formation  may  be  observed  in  cells  of 
undoubted  epithelial  origin,  as,  for  instance,  in  ganglion  cells  and  in 
the  pigment  epithelium  of  the  retina.  An  interesting  proof  that  the 
processes  of  pigmented  connective-tissue  cells  actually  penetrate  the 
epidermis  is  afforded  by  the  case  reported  by  Karg,  of  transplanta- 
tion of  a  piece  of  skin  from  a  white  man  to  a  negro.  After  some 
time  the  piece  of  white  skin  became  pigmented.  Reinke  has  demon- 
strated that  the  pigment  in  certain  cells  is  in  combination  with 
certain  definite  bodies.  The  latter  have  been  given  the  botanical 
name  of  troplwplasts.  If  the  pigment  be  removed,  colorless  tropho- 
plasts  are  left.  They  may  be  tinged  with  certain  stains.  In  the 
epidermis  of  the  white  race  trophoplasts  are  also  constantly  present, 
although  they  are  only  slightly  or  not  at  all  pigmented  (Barlow). 

The  following  may  be  said  concerning  the  vascular  system  of  the 
skin  :  The  arteries  which  supply  the  skin  with  nutriment  penetrate 
the  corium  and  form  a  characteristic  network  in  its  lowest  stratum. 
They  also  anastomose  freely  in  the  fascia  and  the  subcutaneous 
layer.  From  this  plexus  branches  pass  outward  to  form  a  second 
or  subpapillary  plexus.  From  the  latter,  branches  are  again  given 
off  which,  without  further  anastomoses,  pass  along  beneath  the 
rows  of  papillae  and  supply  each  separate  papilla  with  capillary 
twigs.  These  in  turn  pass  over  into  venous  capillaries  which  unite 
and  also  form  several  plexuses,  corresponding  in  general  to  those 
of  the  arterial  system.  The  uppermost  venous  plexus  lies  beneath 
the  papillae,  each  venule  corresponding  to  a  single  row  of  papillae 
and  anastomosing  with  its  neighbors.  The  second  plexus  is  found 
immediately  beneath  the  first,  the  third  in  the  lower  portion  of  the 
corium,  and  the  fourth  at  the  junction  of  the  cutis  and  subcutis. 
Near  the  middle  of  the  subcutis  the  arteries  show  a  circular  muscu- 
lature, but  the  veins  are  already  thus  provided  in  the  network 
between  the  cutis  and  subcutis,  where  they  also  seem  to  possess 
valves.  As  already  stated,  the  subcutaneous  fat  is  divided  into 
lobes  by  transverse  and  longitudinal  bundles  of  connective  tissue  ;  a 
second  system  of  bundles  midway  between  the  cutis  and  fascia 
separates  the  panniculus  adiposus  into  an  upper  and  a  lower  layer. 
The  former  is  supplied  by  direct  arterial  branches  ;  the  latter,  by 
branches  passing  backward  from  the  cutaneous  network.  Those 
regions  which  are  subjected  to  great  external  pressure  are  supplied  by 


348 


THE    SKIN   AND    ITS    APPENDAGES. 


a  greater  number  of  afferent  vessels  the  caliber  of  which  is  increased. 
In  regions  where  the  skin  is  very  mobile  the  arteries  are  greatly 
convoluted.  All  these  vascular  peculiarities  are  present  in  the  new- 
born (Spalteholz). 

The  lymph-vessels  of  the  true  skin  are  also  distributed  in  two 

layers a  deep   and  wide-meshed   plexus   in  the   subcutis,   and   a 

superficial  narrow-meshed  plexus  immediately  beneath  the  papillae. 
Into  the  latter  empty  the  lymph-vessels  coming  from  the  papillae. 
After  treating  the  skin  by  certain  methods,  a  fine  precipitate  may  be 
noticed  here  and  there  in  the  papillary  region  of  the  corium,  a 
proof  that  lymph  clefts  are  present.  These  are  regarded  as  the 
beginnings  of  the  cutaneous  lymphatic  system.  They  may  also  be 


Stratum 
corneum. 


Nerve-fibers 
in  the  epi- 
dermis. 
>  Stratum 
Malpighii. 


H"  -  Papillae. 


Nerve-fiber. 


Fig.  291. — Nerves  of  epidermis  and  papillae  from  ball  of  cat's  foot ;  X  75' 


traced  into  the  epithelium,  where  they  are  in  direct  communication 
with  the  interspinal  spaces  between  the  epithelial  cells  (Unna). 
Cells  are  also  met  with'  in  the  interspinal  spaces  of  the  epidermis  ; 
these  are  migratory  cells,  or  cells  of  Langerhans. 

The  skin  owes  its  great  sensitiveness  to  the  numerous  nerves 
and  special  nerve-endings  present,  not  only  in  the  epithelium,  but 
also  in  the  corium  and  subcutis.  In  certain  regions  of  the  skin  the 
nerves  have  been  traced  into  the  epithelium.  In  the  finger-tip,  for 
instance,  numerous  nerves  are  seen  in  the  epidermis,  where  they 
branch  and  end  in  telodendria  with  or  without  small  terminal  swell- 
ings. There  is  no  direct  communication  between  the  terminal 


THE    SKIN.  349 

nerve  filaments  and  the  epithelial  cells.  (Fig.  291.)  In  certain 
peculiarly  sensitive  regions,  as  the  end  of  the  pig's  snout,  the  nerve- 
fibers  end  in  distinct  saucer-like  discs  (tactile  menisci)  which,  as  a 
rule,  clasp  the  lower  ends  of  the  basal  Malpighian  cells. 

The  special  sensory  nerve -endings  are  situated  in  the  corium 
and  subcutis.  Of  these,  we  may  mention  the  tactile  corpuscles  of 
Meissner,  the  end-bulbs  of  Krause,  the  Pacinian  corpuscles,  Ruf- 
fini's  nerve-endings,  and  the  Golgi-Mazzoni  corpuscles.  All  these 
special  sensory  nerve-endings  with  the  exception  of  the  two  last 
mentioned  have  been  discussed  in  a  former  chapter  (p.  1 54).  Meiss- 
ner's  tactile  corpuscles  are  situated  in  the  tactile  papillae  of  the 
true  skin.  They  are  especially  numerous  in  the  hand  and  foot. 
In  the  distal  phalanx  of  the  index-finger  every  fourth  papilla  is 
a  tactile  papilla,  containing  one  or  sometimes  two  corpuscles  of 


Nerve-fiber.  wtSEflir"   Nerve-fiber' 

--—  Capsule. 

m> 

-  Nerve-fiber. 
-._—  Nerve-fiber. 

Fig.  292. — Meissner' s  corpuscle  from  man  ;       Fig.  293. — Meissner' s  corpuscle  from  man  ; 
X  750.    Technic  No.  295.  X  75°-     Technic  No.  295. 

Meissner.  They  are,  however,  not  nearly  so  numerous  in  other 
parts  of  the  hand  or  in  the  foot.  These  corpuscles  are  further 
found  on  the  dorsal  surface  of  the  hand  and  volar  surface  of  the 
forearm,  in  the  nipple  and  external  genitals,  in  the  eyelids  (border), 
and  in  the  lips.  In  figures  292  and  293  are  shown  two  Meissner's 
corpuscles,  giving  the  appearance  presented  by  these  end-organs 
when  not  stained  with  special  reference  to  nerve  terminations.  For 
the  latter  see  figure  132. 

The  Krause's  end-bulbs,  both  spheric  and  cylindric,  are,  as  a 
rule,  situated  a  short  distance  below  the  papillary  layer,  although 
they  are  frequently  found  in  the  papillae.  They  occur  in  man  in  the 
conjunctiva,  lips,  and  external  genitals,  and  in  the  mucous  mem- 
branes previously  mentioned  (p.  154).  See  page  154  and  figure 
131  for  their  structure. 


350 


THE    SKIN    AND    ITS    APPENDAGES. 


In  the  palm  of  the  hand  and  sole  of  the  foot,  the  subcutaneous 
connective  tissue  contains  numerous  Pacinian  corpuscles.  They 
occur  also  along  the  nerve-fibers  of  the  joints  and  in  the  periosteum 
of  the  extremities.  (See  Fig.  135.) 

Very  recently  Ruffim  demonstrated  in  the  human  corium  the 
existence  of  peculiar  nerve  end-organs,  which  consist  of  a  connec- 
tive-tissue framework  supporting  a  rich  arborization  of  telodendria. 
They  occur  side  by  side  with  the  Pacinian  corpuscles  and  in  appar- 
ently equal  numbers.  These  nerve  terminations  resemble  in  many 
respects  the  neurotendinous  spindles  (see  Fig.  140),  although  they 
present  certain  structural  differences.  Instead  of  intrafusal  tendon 
fasciculi,  the  Ruffmi  end-organ  is  composed  of  white  fibrous  and 
elastic  tissue.  In  this  end-organ  the  medullated  nerves  make 
long  and  tortuous  turns  before  becoming  nonmedullated,  and  |he 

terminations  of  these  nerve-fibers  oc- 
cupy the  whole  of  the  cross-section. 
The  Golgi-Mazzoni  corpuscle  re- 
sembles in  structure  the  Pacinian 
corpuscle,  although  it  possesses  fewer 
lamellae  and  a  relatively  larger  core, 
and  the  nerve  -  fibers  terminating 
therein  are  more  extensively  branched 

fthan  in  the  Pacinian  corpuscle.  Ruf- 
fini  has  found  these  nerve-endings  in 
the  subcutaneous  tissue  of  the  finger- 
tips. 

The  blood  -  vessels  of  the  skin 
are  richly  supplied  with  vasomotor 
nerves,  which  terminate  in  the  non- 
striated  muscle  of  the  vessel  walls. 
These  vasomotor  nerve  -  fibers  are 
neuraxes  of  sympathetic  neurones. 

In  aquatic  birds,  and  more  es- 
pecially in  ducks,  the  waxy  skin  of 

the  beak  and  the  cornified  portion  of  the  tongue  contain  the  so- 
called  corpuscles  of  Herbst,  which  resemble  the  Pacinian  corpuscles 
in  general  structure,  but  have  cubical  cells  in  the  core.  In  the  same 
tissues  are  also  found  the  corpuscles  of  Grandry,  60  f*  long  and 
40  ft  broad.  They  consist  of  a  thin  connective-tissue  capsule,  con- 
taining two  or  three  large  cells.  The  nerve-fiber  retains  its  medul- 
lary sheath  for  some  distance  within  the  capsule.  The  axis-cylinder 
ends  in  discs  situated  between  the  cells  inclosed  by  the  capsule. 


Terminal  disc  of 
—       nerve-fibers. 


Epithelial  cell. 

Connective-tissue 

capsule. 


—  Nerve-fiber. 


Fig.  294. — Grandry' s  corpuscles 
from  bill  of  duck ;  X  5°°-  Technic 
No.  296. 


B.  THE  HAIR. 

The  hair  and  nails  are  regarded  as  special  differentiations  of  the 
skin.  Hair  is  found  distributed  over  almost  the  entire  extent  of  the 
skin,  varying,  however,  in  quantity  and  arrangement  in  different 


THE    HAIR.  351 

regions.  None  whatever  is  present  in  the  palm  of  the  hand  and 
sole  of  the  foot.  In  the  third  fetal  month  small  papillary  elevations 
of  the  skin  are  seen  to  develop  in  those  areas  in  which  the  hairy 
growth  later  appears.  Under  each  of  these  elevations  there  occurs 
a  proliferation  of  the  cells  of  the  Malpighian  layer  downward  into 
the  corium.  Although  the  elevations  soon  disappear,  the  epithelial 
ingrowth  continues  and  finally  forms  the  hair  germ.  This  is  soon 
surrounded  by  a  connective-tissue  sheath  from  the  corium,  in  which 
two  layers  may  be  distinguished.  At  the  lower  end  of  the  hair 
germ  the  corium  is  pushed  upward,  forming  a  papilla  which  pene- 
trates into  the  thickened  bulb  of  the  germ.  This  is  called  the  hair 
papilla.  In  the  mean  time  the  hair  germ  itself  is  undergoing  marked 
differentiation.  An  axial  portion,  forming  later  the  hair  and  inner 
root-sheath,  and  a  peripheral,  constituting  later  the  outer  root- 
sheath,  are  developed.  From  the  latter  are  derived  also  the  first 
traces  of  the  sebaceous  glands,  which  in  the  adult  state  are  in  close 
relationship  to  the  hair  and  empty  their  secretion  into  the  space 
between  the  hair  and  its  sheath.  As  soon  as  the  various  layers  of 
the  hair  are  complete  it  grows  outward,  breaking  through  the  over- 
lying layers  of  the  epidermis. 

The  visible  portion  of  the  hair  is  called  the  hair  shaft,  and 
that  portion  below  the  skin  is  the  hair  root.  The  lower  portion 
of  the  hair  resting  upon  the  papilla  is  known  as  the  hair  bulb, 
and  the  sheaths  encircling  the  root  and  bulb  are  called  the  root- 
sheaths,  the  entire  structure  constituting  the  hair  follicle. 

The  adult  hair  is  covered  by  a  thin  cuticle,  consisting  of  over- 
lying plate-like  cells,  i.i  p.  thick,  most  of  which  possess  no  nuclei. 
Beneath  the  cuticle  is  the  cortical  layer,  composed  of  several  strata 
of  long,  flattened  cells  from  4. 5  //  to  1 1  fj.  broad  and  provided  with 
nuclei.  These  are  also  known  as  the  cortical  fibers  of  the  hair. 
Upon  treatment  with  ammonia  the  fibers  separate  into  delicate 
fibrils,  the  hair  fibrils  (Waldeyer,  82).  Scattered  between  and  within 
the  cells  of  the  cortical  layer  are  varying  quantities  of  pigment 
granules.  The  axial  region  of  the  hair  is  occupied  by  the  medullary 
substance,  from  16  //  to  20  [J.  in  diameter.  This  may  be  lacking  ;  but 
if  present,  consists  of  from  2  to  4  strata  of  polygonal,  nucleated  and 
pigmented  cells.  The  hair  shaft  often  contains  air  vesicles. 

The  inner  root-sheatli  consists  of  three  concentric  layers — first, 
of  an  outer  single  layer  of  clear  nonnucleated  cells,  the  so-called 
layer  of  Henle  ;  second,  of  a  thicker  middle  layer,  made  up  of  two 
strata  of  nucleated  cells  containing  eleidin,  the  layer  of  Huxley ; 
and,  third,  of  an  inner  cuticle,  bordering  upon  the  hair. 

The  outer  root-sheath  is  made  up  of  elements  from  the  stratum 
germinativum.  Here  we  have  to  do  with  prickle  cells,  surrounded 
by  an  outer  layer  of  columnar  elements.  The  connective-tissue 
portion  of  the  hair  follicle  is  composed  of  an  outer,  looser  layer  of 
longitudinal  fibrous  bundles  ;  of  an  inner,  compacter  layer  of  circu- 


352 


THE    SKIN   AND    ITS    APPENDAGES. 


lar  fibers  ;    and   of  an  innermost  well-developed  basement   mem- 
brane— the  glassy  membrane. 

At  a  certain  distance  above  the  root  bulb  all  the  layers  of  the 


The  hair.  Stratum  Malpighii  of  outer  root-sheath. 


•"  Cuticle  of  hair. 
-   Cuticle. 


— •   Huxley's  layer. 
_    Henle's  layer. 


-   Glassy  layer. 


Basal  cells  of 
„ '   the  outer  root- 
sheath. 


—  —  Medulla  of  hair 


Cortical  sub- 
stance of  hair. 


—   Hair  bulb. 


Inner 
root- 
sheath. 


Hair  papilla. 
Blood-vessel. 


Glassy  layer  of 
hair  bulb. 


Connective  tis- 
sue  of  the 
cutis. 


'  295  • — Longitudinal  section  of  human  hair  and  its  follicle  ;    X  about  300. 


epithelial  portion  of  the  hair  follicle  are  well  developed  and  distinct 
from  each  other.     This  condition  changes  toward  the  hair  papilla 


THE    HAIR. 


353 


as  well  as  toward  the  hair  shaft.  Below,  in  the  region  of  the  thick- 
ened hair  bulb,  the  root-sheaths  begin  to  lessen  in  thickness,  their 
layers  becoming  more  and  more  indistinct  toward  the  base  of  the 
hair  papilla.  Finally,  all  differentiation  is  lost  in  the  region  where 
they  encircle  the  neck  of  the  papilla.  Toward  the  shaft  of  the  hair, 
the  root-sheath  also  undergoes  changes.  In  the  region  into  which 
the  sebaceous  glands  empty,  the  inner  root-sheath  disappears,  while 
the  outer  becomes  continuous  with  the  stratum  germinativum  of 
the  epidermis  ;  the  outer  layers  of  the  latter — the  stratum  granu- 
losum,  stratum  lucidum,  and  stratum  corneum — push  downward 
between  the  outer  root-sheath  and  the  hair  to  the  openings  of  the 
sebaceous  glands. 

Regarding  the  growth  of  the  hair,  two  theories  are  prevalent. 


Glassy 
layer. 


Fibrous-tis- 
sue sheath. 


Fig.  296. — Cross- section  of  human  hair  with  its  follicle  ;  X  about  300. 

The  one  theory  assumes  that  the  elements  destined  to  form  the 
epithelial  root-sheaths  are  derived  from  the  epidermis  by  a  constant 
process  of  invagination.  The  component  parts  of  the  hair  would 
thus  be  continuous  with  the  layers  of  the  root-sheaths,  and  conse- 
quently with  those  of  the  epidermis.  Thus  the  basal  cells  of  the 
external  root-sheath  would  extend  over  the  papilla,  and  be  continu- 
ous with  the  cells  of  the  medulla  of  the  hair  (these  relations  are 
especially  well  defined  in  the  rabbit),  and  the  stratum  spinosum 
(middle  layer  of  stratum  Malpighii)  of  the  outer  root-sheath  would 
be  continuous  with  the  cortical  substance  of  the  hair.  According 
to  this  theory  also,  the  layer  of  Henle  would  correspond  to  the 
stratum  lucidum  of  the  epidermis,  and  at  the  base  of  the  hair 
23 


354 


THE    SKIN   AND    ITS   APPENDAGES. 


would  become  its  cuticle,  while  the  layer  of  Huxley  would  form 
the  cuticle  of  the  inner  root-sheath  (Mertsching).  The  other 
theory  assumes  that  the  hair  is  derived  from  a  matrix,  consisting  of 
proliferating  cells  situated  on  the  surface  of  the  papilla.  From 
these  germinal  cells  would  be  derived  the  medullary  and  cortical 
substance  of  the  hair,  its  cuticle,  and  the  inner  root-sheath  (Unna). 
The  shedding  of  hair  is  common  to  all  mammalia,  a  phenomenon 
occurring  periodically  in  the  majority  of  species.  In  man  the  pro- 
cess is  continuous.  Microscopic  examination  shows  that  the  hair 
destined  to  be  shed  becomes  loosened  from  its  papilla  by  a  cornifi- 
cation  of  the  cells  of  its  bulb.  At  the  same  time  the  cortical  por- 
tion of  the  hair  bulb  breaks  up  into  a  brush-like  mass.  Such  hairs 
are  called  bulb  hairs,  in  contradistinction  to  papillary  hairs.  In  the 

region  of  the  former  papilla  there 
arises,  by  a  proliferation  of  the 
external  root-sheath,  a  bud  which 
grows  downward,  from  which  a 
new  hair  with  its  sheaths  and  con- 
nective-tissue papilla  is  developed. 
The  result  is  that  the  developing 
new  hair  gradually  pushes  the  old 
hair  outward  until  the  latter  fin- 
ally drops  out.  The  exact  details 
of  this  process  have  given  rise  to 
considerable  discussion  (vid,  Gotte 
and  Stieda,  87). 

Adjacent  to  the  hair  follicles 
are  bundles  of  smooth  muscle- 
fibers,  known  as  the  arrectores  pi- 
lorum.  They  originate  from  the 
papillary  layer  of  the  corium  and 
extend  to  the  lower  part  of  the 
connective-tissue  sheath  of  the  hair 
follicles.  In  their  course  they  not 
infrequently  encircle  the  sebace- 
ous glands  of  the  follicle.  Since 

the  hair  follicles  have  a  direction  oblique  to  the  skin  surface,  forming 
with  it  an  acute  and  an  obtuse  angle,  and  since  the  muscle  is  situated 
within  the  obtuse  angle,  its  function  may  easily  be  conceived  as 
being  that  of  an  erector  of  the  hair.  The  hair  papillae  are  veiy 
vascular. 

The  nerve-fibers  of  the  hair  follicles  have  recently  been  studied  by 
a  number  of  investigators,  with  both  the  Golgi  and  the  methylene- 
blue  methods.  It  has  been  shown  that  the  hair  follicles  receive 
their  nerve  supply  from  the  nerve-fibers  which  terminate  in  the 
immediate  skin  area.  Each  follicle  receives,  as  a  rule,  only  one 
nerve-fiber,  which  reaches  the  follicle  a  short  distance  below  the 
mouth  of  the  sebaceous  gland.  The  nerve-fiber,  on  reaching  the 


Fig.  297. — Longitudinal  section 
through  hair  and  hair  follicle  of  cat  ; 
X  1 60.  Technic  No.  291. 


THE    NAILS.  355 

follicle,  loses  its  medullary  sheath  and  divides  into  two  branches, 
which  surround  it  in  the  form  of  a  ring.  From  this  complete  or 
partial  ring  of  nerve-fibers  numerous  varicose  fibers  proceed  upward 
parallel  to  the  axis  of  the  follicle  for  a  distance  about  equal  to  the 
cross-diameter  of  the  follicle,  to  terminate,  it  would  seem,  largely 
outside  of  the  glassy  layer  (Retzius).  In  certain  mammalia  the 
nerve-fibers  end  in  tactile  discs,  found  in  the  external  root-sheaths 
of  the  so-called  tactile  hairs.  The  muscles  of  the  hairs  receive 
their  innervation  through  the  neu raxes  of  sympathetic  neurones, 
which  reach  the  periphery  from  the  chain  ganglia  through  the  gray 
rami  communicantes.  These  nerves  are  known  as  pilomotor  nerves, 
and  when  stimulated,  excite  contraction  of  the  erector  muscles  of  the 
hairs,  causing  these  to  assume  an  upright  position  and  producing 
the  appearance  termed  goose  skin,  or  cutis  anserina.  Langley 
and  Sherrington  have  made  interesting  and  important  observations 
on  the  course  and  distribution  of  the  pilomotor  nerves. 


C  THE  NAILS. 

The  nails   are  a  peculiar   modification  of  the  epidermis.     The 
external  arched  portion  is  called  the  body  of  the  nail ;  that  area  upon 

^^  -^.j^we.  --  Stratum 

Nail  wall.--,,          V^r1*"****0"  Stratum 

Nail.-~T:        :3&\  granulo- 

**^sv^  sum- 

Stratum-  -  ^^  ~"  Corium. 

Malpighii.  T^ 

Stratum  cor- — 
neum  of  the 
nail  groove. 

---Blood- 
vessel. 

Fig.  298. — Longitudinal  section  through  human  nail  and  its  nail  groove 
(sulcus)  ;  X  34- 

which  the  latter  rests,  the  nail  bed,  or  matrix ;  and  the  two  folds  of 
epidermis  which  overlap  the  nail,  the  nail  walls.  The  groove  which 
exists  between  the  nail  wall  and  nail  bed  is  known  as  the  sulcus  of 
the  matrix,  and  the  proximal  imbedded  portion  of  the  nail  as  the 
nail  root,  since  all  growth  of  the  nail  takes  place  in  this  region. 
The  nail  bed  consists  of  the  corium,  which  is  here  made  up  of  a 
dense  felt-work  of  coarse  connective-tissue  fibers.  Immediately 
beneath  the  nail  the  corium  is  raised  into  a  number  of  more 
or  less  symmetric  longitudinal  ridges,  which  again  become  con- 
tinuous with  the  connective-tissue  papillae  of  the  skin  at  the  line 
where  the  nail  projects  beyond  its  bed. 

The  depressions  between  the  ridges  are  occupied  by  epidermal 
cells,  which  also  form  a  thin  covering  over  the  ridges  themselves. 


356  THE    SKIN    AND    ITS   APPENDAGES. 

These  cells  correspond  here  to  the  basilar  layer  of  the  stratum  Mal- 
pighii.  The  stratum  granulosum  is  not  uniformly  present,  although 
occurring  as  isolated  areas  in  the  region  of  the  nail  root  and  lunula, 
the  white  area  of  demilunar  shape  at  the  proximal  portion  of  the 
nail.  Unna  has  demonstrated  that  the  pale  color  of  the  lunula  and 
root  of  the  nail  is  due  to  the  presence  of  keratohyalin.  Formerly, 
this  peculiarity  was  attributed  to  a  difference  in  the  distribution  of 
the  vessels  in  the  various  portions  of  the  nail  bed.  The  body  of 
the  nail,  with  the  exception  of  the  lunula,  is  transparent — a  con- 
dition which  may  be  explained  by  the  fact  that  the  elements  of  the 
nail  correspond  to  those  of  the  stratum  lucidum.  As  a  consequence, 
the  vessels  of  the  matrix  shine  through,  except  at  the  lunula,  where 
the  keratohyalin  granules  render  the  nail  opaque. 

The  nail  itself  consists  of  elements  homologous  to  those  of  the 
stratum  lucidum.  They  are  flat,  transparent  cells,  closely  approxi- 
mated, and  all  contain  nuclei.  The  cells  overlie  each  other  like 
tiles,  and  are  so  arranged  that  each  succeeding  lower  layer  projects 

Nail.- 

Stratum  Mal- 
piehii. 
Xail  wall.-;; 

Nail  groove. ..1 


— Corium. 
-—Blood-vessel. 


Fig.  299. — Transverse  section  through  human  nail  and  its  sulcus  ;   X  34- 

a  little  further  distalward  than  the  preceding.  At  the  period  when 
the  nails  are  formed,  about  the  fourth  month  of  fetal  life,  sulci  are 
already  present.  The  first  trace  of  the  nail  is  seen  as  a  marked 
thickening  of  the  stratum  lucidum  in  the  region  which  later  be- 
comes the  body  of  the  nail ;  in  this  stage  the  structure  is  still  cov- 
ered by  the  remaining  layers  of  the  stratum  corneum,  constituting 
the  eppnychium.  The  embryonal  nail  then  spreads  in  all  directions 
until  it  finally  reaches  the  sulcus.  Henceforward  the  growth  is 
uniform.  The  eleidin  normally  present  in  the  stratum  lucidum  of 
the  skin  also  occurs  in  the  nail,  and  is  derived,  as  we  have  already 
seen,  from  the  keratohyalin.  It  may  readily  be  conceived  that  later, 
when  growth  is  confined  to  the  root  of  the  nail,  keratohyalin  is  also 
present.  As  soon  as  the  nail  begins  to  grow  forward,  in  the  ninth 
month,  the  greater  part  of  the  eponychium  is  thrown  off;  but 
during  the  entire  extrauterine  life,  a  portion  of  the  eponychium  is 
retained  at  the  nail  wall,  and  as  hyponychium  on  the  anterior  and 
under  surface  of  the  nail. 


THE    GLANDS    OF    THE    SKIN. 


357 


D.  THE  GLANDS  OF  THE  SKIN. 


the   skin  are  of  two   kinds — sweat-glands  and 
A  modification  of  the  latter  is  seen  in  the  mam- 


Basement 

membrane. 


Fig.  300. — Cross  -  section  of  tubule  of  coiled 
portion  of  sweat-gland  from  human  axilla.  Fixation 
with  sublimate  ;  X  600. 


The   glands  in 
sebaceous  glands, 
mary  glands. 

I.  The  Sweat-glands. — The  sweat-glands,  or  sudoriparous 
glands,  are  distributed 
throughout  the  entire 
skin,  but  are  especially 
numerous  in  certain  re- 
gions— as,  for  instance, 
the  axilla,  palm  of  the 
hand,  and  sole  of  the 
foot.  They  lie  imbedded 
either  in  the  adipose  tis- 
sue of  the  true  skin,  or 
still  deeper  in  the  subcu- 
taneous connective  tissue 
(axilla).  To  this  group 
of  glands  belong  also  the 
ceruminous  glands  of  the 
ear,  the  glands  of  Moll  in 
the  eyelid,  and  the  cir- 
cumanal  glands. 

The  sweat-glands  are  simple  tubular  in  type,  and  their  secreting 
portion  is  coiled  ;  hence  the  name  coil-glands.     The  coil  is,  as  a 

rule,  0.3  or  0.4  mm.  in  di- 
ameter, but  in  the  axilla 
reaches  from  3  to  7  mm. 
The  excretory  duct  (the  su- 
doriferous duct)  is  nearly 
straight  during  its  course  up- 
ward through  the  corium, 
and  always  enters  the  epider- 
mis between  two  papillae  of 
the  corium.  From  here  on, 
its  course  is  spiral,  and  it 
should  be  borne  in  mind  that 
in  its  passage  through  the 
epidermis  it  has  no  other 
wall  than  the  epidermal  cells 
of  the  various  layers  through 
which  it  passes,  although 
these  cells  are  arranged  con- 
centrically around  the  lumen 
of  the  duct.  The  lining  of  the  secretory  or  coiled  portion  of  the  sweat- 
gland  consists  of  cubical  cells  with  finely  granular  protoplasm  and 
round  or  oval  nuclei  possessing  one  or  two  nucleoli.  In  the  excre- 


Nucleus  of 
nonstriated 
muscle-cell. 


Nucleus  of 
gland-cell. 


Fig.  301.  —  Tangential  section  through 
coiled  portion  of  sweat-gland  from  human  axilla. 
Sublimate  fixation  ;  X  7°°- 


358  THE    SKIN   AND    ITS   APPENDAGES. 

tory  segments,  the  cells  are  arranged  in  two  layers.  The  membrana 
propria  is  very  delicate,  and  in  both  regions  of  the  gland  apparently 
structureless.  External  to  the  basement  membrane  is  a  fine  con- 
nective-tissue sheath.  A  marked  peculiarity  of  the  secretory  por- 
tion of  the  gland  consists  in  a  longitudinal  layer  of  smooth  muscle- 
fibers  between  the  membrana  propria  and  the  glandular  epithelium. 
The  presence  of  this  structure  can  be  accounted  for  only  by  assuming 
that  it  is  an  epithelial  derivative. 

The  changes  in  the  gland  cells  during  secretion  have  not  been 
sufficiently  studied,  but  this  much  is  certain,  that  the  secretory  phe- 
nomena are  not  similar  to  those  in  the  sebaceous  glands  (see  below). 
To  the  glandular  secretion  must  be  added  also  the  serum-like 
fluid  oozing  from  the  canalicular  lymph-spaces  in  the  stratum  Mal- 
pighii  into  the  epidermal  portion  of  the  excretory  duct  (Unna). 

The  development  of  the  sweat-glands  begins  in  the  fifth  month 
of  fetal  life.  At  first  solid  cords  grow  from  the  stratum  germi- 
nativum  of  the  epidermis  into  the  corium.  Later,  in  the  seventh 
month,  these  become  hollow. 

Capillary  networks  surround  the  secreting  portions  of  the 
sweat-glands. 

The  nerves  of  the  sweat-glands  have  been  studied  with  the 
aid  of  the  methylene-blue  method  by  Ostroumow,  working  under 
Arnstein's  direction.  These  glands  receive  their  innervation  through 
the  neuraxes  of  sympathetic  neurones,  the  terminal  branches 
of  which  form  an  intricate  network  just  outside  of  the  basement 
membrane,  known  as  the  epilamellar  plexus.  From  this  plexus  fine, 
varicose  nerve-fibers  pass  through  the  basement  membrane,  and, 
after  coursing  a  shorter  or  longer  distance  with  or  without  further 
division,  end  on  the  gland-cells,  often  in  clusters  of  small  terminal 
granules  united  by  delicate  threads. 

2.  The  Sebaceous  Glands. — The  distribution  of  the  sebaceous 
glands  in  the  skin  is  closely  connected  with  that  of  the  hair  follicles 
into  which  they  pour  their  contents.  Exceptions  to  this  rule  occur 
in  only  a  few  regions  of  the  body,  as,  for  instance,  in  the  glans  penis 
and  foreskin  (Tyson's  glands),  in  the  labia  minora,  angle  of  the 
mouth,  glandulae  tarsales,  and  the  Meibomian  glands  of  the  eyelids, 
etc.  As  a  rule  the  sebaceous  gland  empties  by  a  wide  excretory 
duct  into  the  upper  third  of  the  hair  follicle.  The  walls  of  the  duct 
also  produce  secretion,  and  can  therefore  hardly  be  differentiated 
from  the  rest  of  the  gland.  At  its  base  the  duct  widens  and  is  pro- 
vided with  a  number  of  simple  or  branched  alveoli.  The  sebaceous 
glands  are  therefore  of  the  type  of  compound  alveolar  glands,  vary- 
ing in  length  from  0.2  mm.  to  5  mm.  They  are  surrounded  by 
connective -tissue  sheaths,  which  at  the  same  time  cover  the  hair 
follicles.  Inside  of  the  sheath  is  the  membrana  propria,  which  is  a 
continuation  of  the  glassy  membrane  of  the  follicle.  The  two  or 
three  basal  strata  of  glandular  cells  must  be  regarded  as  a  direct 
continuation  of  the  elements  of  the  external  root-sheath.  In  the 


THE  GLANDS  OF  THE  SKIN. 


359 


more  centrally  placed  strata  the  cells  are  distinctly  changed  in  char- 
acter ;  their  contents  consist  of  fat  globules,  varying  in  size  and 
distributed  throughout  the  protoplasm,  giving  this  a  reticular 
appearance,  while  the  nuclei  suffer  compression  from  the  accumu- 
lation of  the  fat  globules  and  gradually  become  smaller  and  more 
angular.  Finally,  the  cells  change  directly  into  secretion,  which  is 
then  poured  into  the  hair  follicle  as  sebum.  It  is  thus  seen  that  in 
the  secretion  of  sebum  the  cells  are  consumed  and  must  be  re- 
placed. This  renewal  takes  place  by  the  constant  proliferation 
of  the  basilar  cells,  which  push  the  remains  of  the  secreting  cells 
upward  and  finally  take  their  places.  The  final  disintegration  of  the 
cells  occurs  either  within  the  gland  itself  or  between  the  hair  follicle 
and  the  hair.  The  secretion  contains  fatty  globules  of  varying 
size,  which  occur  either  free  or  attached  to  cellular  detritus. 


Fig.  302. — Section  of  alveoli  from  sebaceous  gland  of  human  scalp. 

3.  The  Mammary  Glands. — The  mammary  glands  are  also 
included  among  the  cutaneous  glandular  structures.  They  are 
developed  early,  but  not  until  the  fifth  month  is  it  possible  to  dis- 
tinguish a  solid  central  portion,  with  radially  arranged  tubules 
terminating  in  dilatations.  The  structures  are  all  derived  from  the 
basal  layers  of  the  epidermis.  From  birth  to  the  age  of  puberty 
the  organs  are  in  a  state  of  constant  growth,  and  are  early  sur- 
rounded by  a  connective-tissue  sheath.  The  alveoli,  which  have 
been  developed  in  the  mean  time,  are  still  solid  and  relatively  small. 
Up  to  the  twelfth  year  the  glands  remain  identical  in  structure 
in  boys  and  girls.  In  the  female  the  mammary  glands  continue  to 
develop  from  the  age  of  puberty  ;  in  the  male,  on  the  other  hand, 
they  undergo  a  retrograde  metamorphosis,  ending,  finally,  in  the 
atrophy  of  all  except  the  excretory  ducts.  The  mammary  glands 


360 


THE    SKIN   AND    ITS   APPENDAGES. 


do  not  attain  their  full  stage  of  development  in  women  until  the 
last  months  of  pregnancy,  and  are  functionally  active  at  parturition. 
The  human  mammary  gland  when  fully  developed  has  the  fol- 
lowing structure  :  It  consists  of  about  twenty  lobes,  separated  from 
each  other  by  connective-tissue  septa.  These  lobes  are  again 
divided  into  a  larger  number  of  lobules,  and  these  in  turn  are  com- 
posed of  numerous  alveoli,  which,  as  in  the  case  of  the  lung,  pre- 
sent lateral  sacculations.  The  alveoli  are  provided  with  small 
excretory  passages,  which  unite  and  finally  form  the  larger  ducts. 
Shortly  before  terminating  at  the  surface  of  the  mammilla,  each 


_   Alveolus. 


Connective- 
I-     tissue 
stroma. 


Duct  and 
alveoli. 


Adipose  tissue. 

Fig.  303. — From  section  of  mammary  gland  of  nullipara.  (From  Nagel's  "  Die 
weiblichen  Geschlechtsorgane,"  in  "  Handbuchs  der  Anatomic  des  Menschen,"  1896.) 

mammary  duct  widens  into  a  vesicle,  the  sinus  lactiferus.  The 
number  of  excretory  ducts  corresponds  to  that  of  the  larger  lobes. 
The  ducts  are  lined  by  simple  cubical  epithelium,  except  near  the 
termination  in  the  nipple,  where  they  are  lined  by  stratified  pave- 
ment epithelium,  and  surrounded  by  a  fibrous  tissue  sheath. 

The  epithelium  of  the  alveoli  differs  according  to  the  state  of 
functional  activity.  In  a  state  of  rest  it  consists  of  a  single  layer 
of  glandular  cells  of  nearly  cubical  shape  which  stain  deeply,  the 
internal  surfaces  projecting  into  the  lumen.  At  the  beginning 


THE    GLANDS    OF    THE    SKIN.  361 

of  secretion  the  cells  increase  in  length  and  fat  globules  make  their 
appearance  in  their  distal  ends.  At  the  same  time  a  corresponding 
increase  in  size  occurs  throughout  the  entire  alveolus.  Finally,  the 
free  ends  of  the  cells,  which  contain  the  most  fat  globules,  are  con- 
stricted off,  after  which  the  fat  globules  are  freed  in  the  lumen.  The 
secretory  portion  of  the  alveolus  is  then  composed  of  low  epithelial 
cells,  in  which  the  process  begins  anew.  The  process  of  milk  secre- 
tion therefore  consists  in  throwing  off  the  inner  halves  of  the 
cells  containing  the  fat  globules,  and  in  regeneration  of  the  cells 
from  the  nucleated  remains  of  the  glandular  epithelium.  Whether 
a  karyokinetic  division  of  the  nuclei  occurs  in  this  process  is  not 
known,  and  how  often  the  process  of  regeneration  may  be  repeated 
in  a  single  cell  is  not  capable  of  demonstration.  It  is  certain,  how- 
ever, that  entire  cells  are  destroyed,  to  be  replaced  later  by  new 
elements.  The  membrana  propria  of  the  alveoli  appears  homo- 
geneous. Between  it  and  the  glandular  cells  are  so-called  basket 
cells,  similar  to  those  in  the  salivary  glands.  Benda  regards  the 
basket  cells  as  nonstriated  muscle  elements,  having  a  longitudinal 
direction,  making  the  structure  of  the  alveoli  of  the  mammary 
gland  similar  in  this  respect  to  that  of  the  secreting  portion  of  the 
sweat-glands. 

The  skin  of  the  mammilla  is  pigmented,  and  the  papillae  of  its 
corium  are  very  narrow  and  long.  In  the  corium  are  also  found 
large  numbers  of  smooth  muscle-fibers,  which  form  circular  bun- 
dles around  the  excretory  ducts.  In  the  areolae  of  the  mammae 
are  the  so-called  glands  of  Montgomery,  which  very  probably  repre- 
sent accessory  mammary  glands.  These  are  especially  noticeable 
during  lactation. 

The  mammary  glands  possess  many  lymphatics.  These  are 
especially  numerous  in  the  connective-tissue  stroma  between  the 
lobules  and  alveoli.  The  vessels  form  capillary  networks  surround- 
ing the  alveoli.  The  lymph-vessels  collect  to  form  two  or  three 
larger  vessels,  which  empty  into  the  axillary  glands.  The  mam- 
mary gland  receives  its  nerve  supply  from  the  sympathetic  and 
cerebrospinal  nervous  systems  through  the  fourth,  fifth,  and  sixth 
intercostal  nerves.  The  terminations  of  the  nerves  in  the  mammary 
gland  have  been  studied  by  means  of  the  methylene-blue  method 
by  Dmitrewsky,  working  in  the  Arnstein  laboratory,  who  finds  that 
the  terminal  branches  form  epilamellar  plexuses  outside  of  the  base- 
ment membrane  of  the  alveoli,  from  which  fine  nerve  branches  pass 
through  the  basement  membrane  and  end  on  the  gland  cells  in 
clusters  of  terminal  granules  united  by  fine  filaments.  The  nipple 
has  a  rich  sensory  nerve  supply.  In  the  connective-tissue  papillae 
are  found  tactile  corpuscles  of  Meissner. 

The  milk  consists  of  fat  globules  of  varying  size,  which,  how- 
ever, do  not  coalesce — an  attribute  due  to  the  presence  of  albu- 
minous haptogenic  membranes  surrounding  the  globules.  Shortly 
before,  and  for  some  days  after,  parturition  the  milk  contains  true 


362  THE    SKIN   AND    ITS    APPENDAGES. 

nucleated  cells  in  which  are  fat  globules  ;  these  are  known  as  the 
colostrum  corpuscles.  They  probably  represent  cast-off  glandular 
cells  in  a  state  of  fatty  degeneration.  Some  authors  regard  them 
as  leucocytes  which  have  migrated  into  the  lumen  of  the  gland 
and  there  undergone  fatty  degeneration.  This  milk  is  known  as 
colostrum. 

TECHNIC 

287.  Good  general  views  of  the  skin  can  be  obtained  only  from  sections. 
Any  fixation  method  may  be  employed,  although  alcohol  is  preferable  on 
account  of  the  better  subsequent  staining.      For  detail  work  Flemming's 
solution,  corrosive  sublimate,  or  osmic  acid  is  the  best.      Sectioning  of  the 
skin  is  attended  with  many  difficulties,  and  large  pieces  can  be  cut  only 
in  celloidin.     Small  and  medium-sized  pieces  may  be  cut  in  paraffin  ;  but 
even  in  this  case  the  skin  must  be  rapidly  imbedded  in  the  paraffin — /.  e. , 
it  must  not  remain  too  long  in  either  alcohol  or  toluol — and  the  paraffin 
must  have  only  the  consistency  necessary  to  cut  well  (about  50°  C.  melting- 
point).     In  order  to  obtain  good  paraffin  sections  of  the  skin  the  follow- 
ing procedure  is  recommended :   Pieces  fixed  in  Flemming's  solution  or 
osmic  acid  are  kept  in  96%  alcohol,  then  placed  for  not  more  than  twenty- 
four  hours  in  absolute  alcohol  and  imbedded  in  paraffin  by  means  of  the 
chloroform  method.     In  the  chloroform,   chloroform -paraffin,  and  pure 
paraffin  they  remain  for  one  hour  each.     The  paraffin  used  should  consist  of 
two  parts  paraffin  of  42°  C.,  and  one  part  paraffin  of  50°  C.  melting-point. 
The  thermostat  must  be  kept  at  50°   C.    (R.   Barlow).     The  sections 
should  not  be  mounted  by  the  water-albumen  method. 

288.  In  sections  of  epidermis  which  have  been  freshly   fixed  with 
osmic  acid,  the  stratum  corneum  may  be  clearly  differentiated  into  three 
layers  (probably  because  of  the  defective  penetration  of  the  reagent) — 
into  a  blackened  superficial,  a  middle  transparent,  and  a  still  lower  black 
layer  (vid.  Fig.  304). 

289.  In  tissue  fixed  in  alcohol  or  corrosive  sublimate  the  stratum 
lucidum  stains  yellow  with  picrocarmin,  but  is  very  weakly  colored  by 
basic  anilin  stains.     In   unstained  preparations  the  stratum  lucidum  is 
glass-like  and  transparent.     Eleidin  is  diffusely  scattered  throughout  both 
the  stratum  lucidum  and  stratum  corneum.      Like  keratohyalin,  it  stains 
with  osmic  acid  and  also  with  picrocarmin,  but  not  with  hematoxylin. 
Nigrosin  stains  eleidin,  but  not  keratohyalin. 

290.  Keratohyalin  is  insoluble  in  boiling  water  and  is  not  attacked 
by  weak  organic  acids.     It  dissolves,  however,  in  boiling  acetic  acid,  but 
is  not  changed  by  the  action  of  pepsin  or  trypsin.      The  keratohyalin 
granules  of  the  stratum  granulosum  swell  in  from  i  %  to  5  %  potassium- 
hydrate  solution  ;  under  the  influence  of  heat  these  granules  together  with 
the  cells  containing  them  are  finally  dissolved.     They  are  not  attacked 
by  ammonia,  and  remain  unaffected  for  a  long  time  in  strong  acetic  acid. 
As  ammonia  and  acetic  acid  render  the  remaining  portions  of  the  tissue 
transparent,  these  reagents  may  be  employed  for  the  rapid  identification 
of  keratohyalin.     The  larger  flakes  of  keratohyalin  swell  in  sodium  car- 
bonate solution  (i%),  but  not  the  smaller  granules,  and  it  would  seem 
that  the  larger  granules  have  less  power  of  resistance  than  the  smaller. 
Keratohyalin  remains  unchanged  in  alcohol,  chloroform,  and  ether,  but 


TECHNIC. 


363 


is  digested  in  trypsin  and  pepsin  (not,  however,  the  keratin).  Kerato- 
hyalin  can  be  stained  with  hematoxylin  and  most  of  the  basic  anilin  dyes. 
291.  The  prickles  of  the  cells  composing  the  stratum  Malpighii  may 
be  seen  in  very  thin  sections  (not  over  3  /*  in  thickness)  of  skin  previ- 
ously fixed  in  osmic  acid.  In  this  case  it  is  best  to  employ  not  Canada 
balsam,  but  glycerin,  which  does  not  have  so  strong  a  clearing  action. 
Isolation  of  the  prickle  cells  is  best  accomplished  as  follows  (Schieffer- 
decker)  :  A  fresh  piece  of  epidermis  is  macerated  for  a  few  hours  in  a 
filtered,  cold-saturated,  aqueous  solution  of  dry  pancreatin ;  the  whole 
may  then  be  preserved  for  any  length  of  time  in  equal  parts  of  glycerin, 


Outer  dark  layer. 

Stratum  corneum. 
Middle  light  layer. 

Inner  dark  layer. 
Stratum  lucidum. 

Stratum  Malpighii. 


Kkl 

b  — 


Cutis  and  sub- 
cutis. 

Fat  cell. 


Fig.  304. — Transverse  section  through  the  human  skin.  Treated  with  osmic  acid  ; 
X  30  :  a,  Part  of  the  tortuous  duct  of  a  sweat-gland  in  the  epidermis  ;  ^,  duct  of  same 
sweat-gland  in  the  corium. 


water,  and  alcohol.      Small  pieces  taken  from  such  specimens  are  readily 
teased  and  show  both  isolated  and  small  groups  of  attached  prickle  cells. 

292.  The  distribution  of  the  pigment  in  the  skin  is  best  studied  in 
unstained  sections.     With  a  nearly  closed  diaphragm  and  under  medium 
magnification  the  pigment  granules  appear  darker  on  raising  the  tube  and 
lighter  upon  lowering  it. 

293.  In  sections  of  skin  treated  with  Flemming's  fluid,  the  structure 
of  the  cutis  also  may  be  studied.     The  medullary  sheaths  of  the  nerve- 
fibers  and  the  fat  appear  black.      In  preparations  stained  with  safranin  the 


364  THE    SKIN   AND    ITS   APPENDAGES. 

elastic    fibers   are   colored   red   and   are    very    distinct    (Stohr  and   O. 
Schultze).     For  the  orcein  method  according  to  Unna,  see  T.  138. 

294.  Hair  may  be  examined  in  water  without  further  manipulation. 
The  cuticle  is  then  seen  to  consist  of  polygonal  areas,  the  border-lines  of 
which  correspond  to  the  limits  of  the  flattened  cells.      By  slightly  lower- 
ing the  objective  the  cortical  substance  comes  into  view  with  its  indistinct 
striation  and  occasional  pigmentation.    The  medullary  substance,  if  pres- 
ent, may  also  be  seen  with  its  vesicles  containing  air.      Both  the  cortical 
and  cuticular  cells  may  be  isolated,  the  process  consisting  in  treating  the 
hairs  for  several  days  with  33  %  potassium  hydrate  solution  at  room  tem- 
perature, or  in  heating  the  whole  for  a  few  minutes.      Concentrated  or 
weak  sulphuric  acid  produces  the  same  result.    On  warming  a  hair  in  sul- 
phuric acid  until  it  begins  to  curl  and  then  examining  it  in  water,  we  find 
that  the  cortical  and  medullary  layers  as  well  as  the  cuticle  are  separated 
into  their  elements.     Treatment  of  the  skin  with   Muller's  fluid,  alco- 
hol, or  sublimate  is  recommended  for  the  examination  of  hair  and  hair 
follicles.     The  orientation   of  the  specimen  should  be  very  precise,  in 
order  to  obtain  exact  longitudinal  or  cross-sections  of  the  hair.     There 
is  hardly  a  structure   of  the  body  which  is  more  suitable   for  staining 
with  the  numerous  coal-tar  colors  than  the  hair  and  its  follicle  (Merkel). 

295.  The  corpuscles  of  Meissner  may  be  best  obtained  from  the  end 
of  the  finger.     After  boiling  a  piece  of  fresh  skin  from  the  finger-tip  for 
about  a  quarter  of  an  hour,  the  epidermis  may  be  easily  removed ;    the 
papillae  are  now  seen  on  the  free  surface  of  the  cutis.     A  portion  of  the 
latter  is  cut  away  with  a  razor  and  examined  in  a  3%  solution  of  acetic 
acid.     The  corpuscles  are  readily  distinguished.     Their  relations  to  the 
nerves  should  be  studied  in  specimens  fixed  with  osmic  acid  or  gold 
chlorid.     The  terminations  of  the  nerves  in  these  end -organs  are  best  seen 
in  preparations  stained  after  the  infra  vitam  methylene-blue  method. 

296.  The  corpuscles  of  Herbst  and  Grandry  are  found  in  the  waxy 
skin  covering  the  bill,  and  in  the  palate  of  the  duck  (especially  numerous 
in  the  tongue  of  the  woodpecker).      For  the  study  of  the  nervous  ele- 
ments  the  following  method  is  useful  :    Pieces  of   the  waxy  skin   are 
removed  with  a  razor  and  placed  for  twenty  minutes  in  50%  formic  acid. 
After  washing  the  specimens  for  a  short  time  in  distilled  water  they  are 
transferred  to  a  small  quantity  of  i%  gold  chlorid  solution  (twenty  min- 
utes), then  again  rinsed  in  distilled  water,  and  placed  for  from  twenty- 
four  to  thirty-six  hours  in  the  dark  in  a  large  quantity  (^   liter)   of 
Pichard's  solution  (amyl  alcohol   i   part,  formic  acid  i  part,  water  TOO 
parts).     After  again  washing  in  water  the  specimens  are  transferred  to 
alcohols  of  gradually  increasing  strengths  and  finally  imbedded  in  celloidin 
or  celloidin -paraffin. 

297.  The  Pacinian  corpuscles  occur  in  the  mesentery  of  the  cat  and 
may  be  examined  in  physiologic  saline  solution. 

298.  The  nerves  of  the   epidermis  are  demonstrated  by  the  gold- 
chlorid  method  (see  p.  166) .     But  even  here  the  chrome -silver  method  and 
the  intra  vitam  methylene-blue  method  yield  extremely  good  results,  and 
may  be  used  with  great  advantage  in  the  study  of  the  nerves  in  the  cutis. 

299.  The  so-called  tactile  menisci  are  very  numerous  in  the  snout  of 
the  pig  and  the  mole.     Bonnet  recommends  for  these  structures  fixation  in 
°-33%  chromic  acid  solution  (yid.  T.  26),  overstaining  with  hematoxylin, 
and  differentiation  in  an  alcoholic  solution  of  potassium  ferricyanid. 


THE    SPINAL    CORD.  365 


VII.  THE  CENTRAL  NERVOUS  SYSTEM. 

IN  a  study  of  the  minute  anatomy  of  the  central  nervous  system 
consideration  should  be  given  to  the  arrangement  of  the  nerve-cells 
and  nerve-fibers  in  the  various  regions,  and  to  the  mutual  relations 
which  the  elements  of  the  nervous  system  bear  to  one  another.  In 
a  text -book  of  this  scope,  however,  we  shall  be  unable  to  enter  into 
the  consideration  of  these  subjects  in  detail,  but  must  content  our- 
selves with  a  very  general  discussion  of  the  structure  of  certain 
regions  of  the  central  nervous  system  and  an  account  of  a  few  typical 
examples  illustrating  the  mutual  relationship  of  the  nerve-elements 
to  one  another.  We  shall,  therefore,  give  a  general  description  of 
the  structure  of  the  spinal  cord,  cerebellum,  cerebrum,  olfactory 
lobes,  and  ganglia.  In  this  description  we  have  drawn  freely 
from  the  results  of  the  researches  of  Golgi  (94),  Ramon  y  Cajal 
(93 »  0»  von  Lenhossek  (95),  Kolliker  (93),  and  van  Gehuchten 
(96).  ' 

A.  THE  SPINAL  CORD. 

The  spinal  cord  extends  from  the  upper  border  of  the  atlas  to 
about  the  lower  border  of  the  first  lumbar  vertebra.  It  has  the  form 
of  a  cylindric  column,  which  at  its  lower  end  becomes  quite  abruptly 
smaller,  to  form  the  conns  medullaris,  and  terminates  in  an  attenu- 
ated portion — the  filum  terminate .  It  presents  two  fusiform  enlarge- 
ments, known  as  the  cervical  and  lumbar  enlargements  respectively. 
The  spinal  cord  is  partly  divided  into  two  symmetric  halves  by  an 
anterior  median  fissure  and  by  a  septum  of  connective  tissue,  extend- 
ing into  the  substance  of  the  cord  from  the  pia  mater  (one  of  the 
fibrous  tissue  membranes  surrounding  the  cord),  and  known  as  the 
posterior  median  septum.  Structurally  considered,  the  spinal  cord 
consists  of  white  matter  (mainly  medullated  nerve-fibers)  and  gray 
matter  (mainly  nerve-cells  and  medullated  nerve-fibers).  The  white 
and  the  gray  matter  present  essentially  the  same  general  features  at 
all  levels  of  the  spinal  cord,  although  the  relative  proportion  of  the 
two  substances  varies  somewhat  at  different  levels.  The  different 
portions  of  the  cord  present  also  certain  structural  peculiarities. 

The  distribution  of  the  gray  and  the  white  substances  of  the 
spinal  cord  is  best  seen  in  transverse  sections. 

The  varying  shape  of  the  spinal  cord  in  the  several  regions  and 
the  changing  relations  of  the  gray  to  the  white  substance  are  shown 
in  the  illustrations  of  cross-sections  of  the  adult  human  spinal 
cord  (see  p.  366). 

The  gray  substance  is  arranged  in  the  form  of  two  crescents, 
one  in  each  half  of  the  cord,  united  by  a  median  portion  extending 
from  one  half  of  the  cord  to  the  other,  the  whole  presenting  some- 
what the  form  of  an  H.  The  horizontal  part  contains  the  commis- 


366 


THE   CENTRAL    NERVOUS    SYSTEM. 


Fig-  3°5-— Four  cross-sections  of  the  human  spinal  cord  ;  X  7  :  A,  Cervical  region 
in  the  plane  of  the  sixth  spinal  nerve-root ;  B,  lumbar  region  ;  C,  thoracic  region  ;  Z>, 
sacral  region  (compare  with  Fig.  306).  (From  preparations  of  H.  Schmaus.) 


THE   SPINAL    CORD.  367 

surcs  and  the  central  canal  of  the  spinal  cord,  while  the  vertical 
limbs  or  crescents  extend  to  the  ventral  and  dorsal  nerve-roots, 
forming  the  anterior  and  posterior  horns.  The  former  are,  as  a 
rule,  the  larger,  and  at  their  sides  (laterally)  the  so-called  lateral 
horns  may  be  seen,  varying  in  size  in  different  regions.  In  each 
anterior  horn  are  three  main  groups  of  ganglion  cells  :  the  ventro- 
lateral,  made  up  of  root  or  motor  nerve-cells  ;  the  ventromesial, 
composed  of  commissural  cells  ;  and  the  lateral  (in  the  lateral 
horn),  containing  column  cells.  At  the  median  side  of  the  base 
of  each  posterior  horn  we  find  a  group  of  cells  and  fibers  known 
as  the  column  of  Clark,  most  clearly  defined  in  the  dorsal  region, 
while  in  the  posterior  horn  itself  is  the  gelatinous  substance  of 
Rolando.  Aside  from  these,  numerous  cells  and  fibers  are  scat- 
tered throughout  the  entire  gray  substance. 

The  motor  nerve-cells  lie  in  the  ventrolateral  portion  of  the  ante- 
rior horn,  their  neuraxes  extending  into  the  anterior  nerve-root. 
Their  dendrites  are  distributed  in  a  lateral,  dorsal,  and  mesial  direc- 
tion, the  two  former  groups  ending  in  the  anterior  and  lateral  col- 
umns, the  mesial  in  the  region  of  the  anterior  commissure.  Some 
of  the  mesial  dendrites  extend  beyond  the  median  line  and  form  a 
sort  of  commissure  with  the  corresponding  processes  of  the  other 
side.  The  commissural  cells  lie  principally  in  the  mesial  group  of 
the  anterior  horn,  but  occur  here  and  there  in  other  portions  of  the 
gray  substance.  Their  neuraxes  form  the  anterior  gray  commis- 
sure with  the  corresponding  processes  from  the  other  side.  After 
entering  the  white  substance  of  the  other  side,  these  neuraxes 
undergo  a  T-shaped  division,  one  branch  passing  upward  and  the 
other  downward.  The  column  cells  are  small  multipolar  elements, 
represented  by  the  cells  of  the  lateral  horns,  although  they  are 
also  found  throughout  the  entire  gray  mass.  Their  neuraxes  pass 
directly  into  the  anterior,  lateral,  and  posterior  horns. 

The  cells  of  the  column  of  Clark,  or  micleus  dorsalis,  are  of  two 
kinds — those  in  which  the  neuraxes  pass  to  the  anterior  commis- 
sure (commissural  cells)  and  those  in  which  the  neuraxes  pass  into 
the  direct  cerebellar  tract  of  the  same  side.  The  plurifunicular 
cells  are  cells  the  neuraxes  of  which  divide  two  or  three  times  in 
the  gray  substance,  the  branches  then  passing  to  different  columns 
of  the  white  matter  on  the  same  or  opposite  side  of  the  cord.  In 
the  latter  case  the  branches  must  necessarily  extend  through  the 
commissure.  The  cells  of  the  substantia  gelatinosa  (Rolando)  are 
cells  with  short,  freely  branching  neuraxes,  which  end  after  a  short 
course  in  the  gray  mass  (Golgi's  cells).  The  posterior  horn  con- 
tains marginal  cells,  spindle-shaped  cells,  and  stellate  cells.  The 
first  are  situated  superficially  near  the  extremity  of  the  posterior 
horn,  their  neuraxes  extending  for  some  distance  through  the  gela- 
tinous substance  of  Rolando  and  then  into  the  lateral  column.  The 
spindle-shaped  cells  are  the  smallest  in  the  spinal  cord  and  possess  a 
rich  arborization  of  dendrites  extending  to  the  nerve -root  of  the  pos- 


368 


THE    CENTRAL    NERVOUS    SYSTEM. 


terior  horn.  Their  neuraxes,  which  originate  either  from  the  cell- 
body  or  from  a  dendrite,  pass  over  into  the  posterior  column.  The 
stellate  cells  are  supplied  with  dendrites,  which  either  branch  in 
the  substance  of  Rolando  or  extend  into  the  column  of  Burdach. 

The  gray  matter  contains,  further;  numerous  medullated  nerve- 
fibers,  in  part  the  neuraxes  of  the  nerve-cells  previously  mentioned, 
and  in  part  collateral  and  terminal  branches  of  the  nerve-fibers  of 
the  white  matter  with  their  telodendria ;  also  supporting  cells, 
known  as  neurogliar  cells  (to  be  discussed  later),  and  blood-vessels. 

The  white  matter  of  the  spinal  cord  consists  of  medullated  fibers, 
which  are  devoid  of  a  neurilemma,  of  neurogliar  tissue,  and  of  fibrous 
connective  tissue. 

In  each  half  of  the  cord  the  white  substance,  which  surrounds 
the  gray,  is  separated  by  the  gray  matter  and  its  nerve -roots  into 


Posterior    horn    

cell. 

Crossed  pyram- 
idal column. 

Golgi     cell     of 

posterior  horn. 

Direct   cerebel- 
lar  column. 
Column  cells. 

Golgi'scommis- 
sural  cells. 

Gowers' 

column. 
Motor  cells.    — 


Collaterals 
of  crossed 
pyramidal 
column. 


Collaterals 
ending  in 
the  gray 
matter. 


Direct  pyramidal  column. 

Fig.  306. — Schematic  diagram  of  the  spinal  cord  in  cross-section  after  von  Lenhos- 
sek,  showing  in  the  left  half  the  cells  of  the  gray  matter,  in  the  right  half  the  collateral 
branches  ending  in  the  gray  matter. 


three  main  divisions  or  columns:  The  first  division,  lying  between 
the  anterior  median  fissure  and  the  anterior  horn,  is  the  anterior 
column ;  the  second,  lying  between  the  anterior  and  posterior 
horns,  is  the  lateral  column  (since  the  anterior  and  lateral 
columns  belong  genetically  to  each  other,  the  term  anterolat- 
eral  column  is  often  used)  ;  and  the  third,  lying  between  the  poste- 
rior nerve-root  and  the  posterior  median  septum,  is  the  posterior 
column. 

By  means  of  certain  methods  it  has  been  possible  to  separate 
the  white  substance  into  still  smaller  divisions,  the  most  important 
of  which  may  here  be  described. 

In  each  anterior  column  is  found  a  narrow  median  zone  extend- 
ing along  the  entire  length  of  the  anterior  median  fissure  and  con- 


THE  SPINAL   CORD. 


24 


370  THE    CENTRAL    NERVOUS    SYSTEM. 

taining  nerve-fibers  which  come  from  the  pyramids  of  the  medulla. 
The  majority  of  the  pyramidal  fibers  cross  from  one  side  of  the  cord 
to  the  other  in  the  lower  portion  of  the  medulla,  at  the  crossing  of 
the  pyramids,  and  form  a  large  bundle  of  nerve-fibers  found  in  each 
lateral  column,  which  will  receive  attention  later.  Some  of  the 
pyramidal  fibers  descend  into  the  cord  on  the  same  side,  to  cross  to 
the  opposite  side  at  different  levels  in  the  cord.  These  latter  fibers 
constitute  the  narrow  median  zone,  on  each  side  of  the  anterior 
median  fissure  previously  mentioned,  forming  the  anterior  or  direct 
pyramidal  tract,  or  the  column  of  Tiirck.  Between  the  direct 
pyramidal  tract  and  the  anterior  horn  lies  the  anterior  ground 
bundle. 

In  the  lateral  columns  are  found  a  number  of  secondary  col- 
umns, which  may  now  be  mentioned.  In  front  of  and  by  the  side 
of  the  posterior  horn  in  each  lateral  column  lies  a  large  group  of 
nerve-fibers,  forming  a  bundle  which  varies  somewhat  in  size  and 
shape  in  the  several  regions  of  the  spinal  cord,  but  which  has  in 
general  an  irregularly  oval  outline.  These  nerve-fibers  are  the 
pyramidal  fibers,  previously  mentioned,  which  in  the  lower  part  of 
the  medulla  cross  from  one  side  to  the  other,  and  for  this  reason 
are  known  as  the  crossed  pyramidal  fibers,  forming  the  crossed 
pyramidal  columns.  External  to  these  columns  and  to  the  poste- 
rior horns,  and  extending  from  the  posterior  horns  half-way  around 
the  periphery  of  the  lateral  columns,  lie  the  direct  cerebellar  col- 
umns, consisting  of  the  neuraxes  of  the  cells  of  the  columns  of 
Clark,  which  have  an  ascending  course.  Lying  just  external  to  and 
between  the  anterior  and  posterior  horns  is  a  somewhat  irregular 
zone,  the  mixed  lateral  column,  containing  several  short  bundles 
of  fibers,  the  anterior  of  which  are  probably  motor  ;  the  posterior, 
sensory.  In  the  ventrolateral  portions  of  the  lateral  columns, 
between  the  mixed  lateral  and  the  direct  cerebellar  columns  and 
extending  as  far  backward  as  the  crossed  pyramidal  columns,  lie 
two  not  well-defined  columns,  known  as  the  ascending  anterolat- 
eral  or  Gowers's  columns  and  the  descending  anterolateral  col- 
umns ;  the  former  are  nearer  the  outer  portion  of  the  cord. 

In  the  posterior  column  we  distinguish  a  median  and  a  lateral 
column.  The  former  lies  along  the  posterior  median  septum,  and 
may  even  be  distinguished  externally  by  an  indentation  ;  its  upper 
portion  tapers  into  the  fasciculus  gracilis.  This  is  the  column  of 
Goll,  and  it  contains  ascending  or  centripetal  fibers.  The  lateral 
tract  lies  between  the  column  of  Goll  and  the  posterior  horn,  and 
is  known  as  the  column  of  Burdach,  posterior  ground-bundle,  or 
posterolateral  column.  It  contains  principally  the  shorter  tracts,  or 
bundles  of  longitudinal  fibers  connecting  the  adjacent  parts  of  the 
spinal  cord  with  one  another. 

Many  of  the  nerve-fibers  of  the  posterior  column  are  the  neu- 
raxes of  spinal  ganglion  cells  which  enter  the  spinal  cord  through 
the  posterior  roots.  The  cell-bodies  of  the  spinal  ganglion  or  sen- 


THE   SPINAL    CORD.  3/1 

sory  neurones  are  situated  in  the  spinal  ganglia  found  on  the  pos- 
terior roots  of  the  spinal  nerves.  In  the  embryo  they  are  distinctly 
bipolar,  but  during  further  development  their  two  processes  approach 
each  other,  and  then  fuse  for  a  certain  distance,  forming  finally 
single  processes  which  branch  like  the  letter  T.  In  reality,  then, 
there  are  two  processes  which  are  fused  for  a  certain  distance  from 
the  cell-body  of  each  neurone.  The  peripherally  directed  process 
is  regarded  as  the  dendrite  of  the  cell,  and  the  proximal  as  the 
neuraxis  passing  to  the  spinal  cord.  The  neuraxes  enter  the  spinal 
cord  through  the  posterior  roots  and  pass  to  the  posterior  columns, 
where  they  divide,  Y-shaped,  into  ascending  and  much  shorter 
descending  branches,  from  each  of  which  numerous  collateral 
branches  are  given  off. 

From  the  preceding  account  of  the  white  matter  of  the  spinal 
cord,  it  may  be  seen  that  it  consists  of  longitudinally  directed  neu- 
raxes arranged  in  so-called  short  and  long  tracts  or  columns.  The 
neuraxes  constituting  the  former,  after  a  short  course  through  the 
gray  matter,  emerge  from  it,  and  after  giving  off  various  collaterals, 
again  penetrate  into  the  gray  matter,  where  their  telodendria  enter 
into  contact  with  the  ganglion  cells.  The  long  columns  consist  of 
the  neuraxes  of  neurones  the  cell-bodies  of  which  are  situated  in 
the  cerebrum  or  cerebellum,  and  of  neurones  the  cell-bodies  of  which 
are  in  the  spinal  cord  or  spinal  ganglia  and  the  neuraxes  of  which 
terminate  in  the  medulla  or  cerebellum.  The  nerve-fibers  of  the 
various  columns  give  off  numerous  collaterals  which  enter  the  gray 
matter  to  end  in  telodendria.  The  collaterals  of  the  posterior  col- 
umns end  :  (i)  between  the  cells  of  the  gelatinous  substance  of  the 
posterior  horns  ;  (2)  in  the  columns  of  Clark  ;  (3)  in  the  anterior 
horns,  these  constituting  the  principal  portion  of  the  so-called  reflex 
bundles  ;  (4)  in  the  posterior  horn  of  the  opposite  side.  The  col- 
laterals of  the  lateral  columns  pass  horizontally  toward  the  central 
canal,  some  ending  in  the  anterior  horn,  others  closely  arranged 
near  the  columns  of  Clark,  and  some  arching  around  the  central 
canal,  forming  with  the  corresponding  fibers  of  the  other  side  the 
anterior  bundles  of  the  posterior  commissure.  The  collaterals  of 
the  anterior  columns  form  well-marked  plexuses  in  the  anterior 
horns  of  the  same  and  opposite  -sides. 

We  have  still  to  describe  the  two  commissures.  The  anterior 
consists  of:  first,  neuraxes  from  the  commissural  cells;  second, 
dendrites  from  the  lateral  group  of  the  anterior  horn  cells  ;  and, 
third,  the  collaterals  of  the  anterolateral  column,  which  end  in  the 
gray  substance  of  the  other  side  of  the  cord.  The  posterior  com- 
missure is  probably  composed  of  the  collaterals  from  all  the  remain- 
ing columns.  The  posterior '  bundle  of  this  commissure  comes 
from  the  posterior  column  ;  the  middle,  from  the  posterior  portion 
of  the  lateral  column  ;  and  the  anterior,  or  least  developed,  from 
the  anterior  portion  of  the  lateral  column,  possibly  also  from  the 
anterior  column. 


372 


THE    CENTRAL    NERVOUS    SYSTEM. 


In  the  gray  commissure,  nearer  its  anterior  border,  is  situated 
the  central  canal  of  the  spinal  cord,  continuous  above  with  the 
ventricular  cavity  of  the  medulla  and  terminating  caudally  in  the 
filum  terminale.  This  canal  is  not  patent  in  the  majority  of  adults, 
being  occluded  from  place  to  place.  The  canal  is  lined  by  a  layer 
of  columnar  cells,  developed  from  columnar  cells,  known  as  spongio- 
blasts,  lining  the  relatively  larger  canal  of  the  embryonic  spinal 
cord.  In  young  individuals  these  cells  are  ciliated  and  their  basal 
portions  terminate  in  long,  slender  processes. 


B.  THE  CEREBELLAR  CORTEX. 

In  the  cerebellar  cortex  we  distinguish  three  general  layers — 
the  outer  molecular,  the  middle  granular  (rust-colored  layer),  and 
the  inner  medullary  tract 


^r" ^Dendrite. 


Blood-vessel 


?•• — Nerve-fiber  layer. 


Fig.  308. — Section  through  the  human  cerebellar  cortex  vertical  to  the  surface  of  the  con- 
volution.    Treatment  with  Miiller's  fluid;  X  IJ5- 

The  molecular  layer  contains    three  varieties   of  nerve-cells, 
those  of  Purkinje,  which  border  upon  the  granular  layer,  the  stel- 


374 


THE    CENTRAL    NERVOUS    SYSTEM. 


late  cells,  and  the  small  cortical  cells.  The  cells  of  Purkinje  pos- 
sess a  large  flask-shaped  body  (about  60  fJ.  in  diameter),  from  which 
one  or  more  well-developed  dendrites  pass  toward  the  periphery. 
The  latter  branch  freely  and  the  main  arborization  has  in  each  case 
the  general  shape  of  a  pair  of  deer's  antlers.  These  dendrites 
extend  nearly  to  the  periphery  of  the  cerebellar  cortex.  In  a 
section  horizontal  to  the  surface  of  the  organ  the  dendrites  of  the 
Purkinje's  cells  are  seen  to  lie  in  a  plane  very  nearly  vertical  to  the 
surface  of  the  convolutions,  so  that  a  longitudinal  section  through 
the  latter  would  show  a  profile  view  of  the  cells.  In  other  words, 
they  have  an  appearance  much  like  that  of  a  vine  trained  upon  a 
trellis.  The  neuraxes  of  the  cells  of  Purkinje  arise  from  their  basal 


•'*--  Dendrite. 


—  Cell-body. 


Neuraxis. 


—  Neuraxis. 


Fig.  310. — Cell  of  Purkinje  from  the  human  cerebel- 
lar cortex.       Chrome-silver  method  ;  X  I2°- 


—  Claw-like    telo- 
dendrion  of 
dendrite. 


Fig.  311. — Granular  cell 
from  the  granular  layer  of  the  hu- 
man cerebellar  cortex.  Chrome- 
silver  method  ;  X  Io°- 


(inner)  ends  and  extend  through  the  granular  layer  into  the  medul- 
lary substance.  During  their  course  they  give  off  a  few  collaterals, 
which  pass  backward  to  the  molecular  layer  and  end  in  telodendria 
near  the  bodies  of  the  cells  of  Purkinje.  The  stellate  cells  lie  in 
various  planes  of  the  molecular  layer.  Their  peculiar  interest  lies 
in  the  character  of  their  neuraxes.  The  latter  are  situated  in  the 
same  plane  as  the  dendrites  of  the  cells  of  Purkinje,  run  parallel  to 
the  surface  of  the  convolution,  and  possess  two  types  of  collaterals. 
Those  of  the  first  are  short  and  branched  ;  those  of  the  second 
branch  at  a  level  with  the  cells  of  Purkinje,  and  form,  together 
with  their  telodendria,  basket-like  nets  around  the  bodies  of  these 
ceJJ,s.  The  small  cortical  cells  of  the  molecular  layer  are  found 


THE  CEREBRAL  CORTEX.  375 

in  all  parts  of  this  layer,  but  are  more  numerous  in  its  peripheral 
portion.  They  are  multipolar  cells  with  neuraxes  which  are  not 
readily  stained  and  concerning  the  fate  of  which  little  is  known. 

The  granular  layer  contains  two  varieties  of  ganglion  ele- 
ments, the  so-called  granular  cells  (small  ganglion  cells)  and  the 
large  stellate  cells.  The  dendrites  of  the  granular  cells  are  short, 
few  in  number  (from  three  to  six),  branch  but  slightly,  and  end  in 
short,  claw-like  telodendria.  Their  neuraxes  ascend  vertically  to 
the  surface  and  reach  the  molecular  layer.  At  various  points  some 
of  them  are  seen  to  undergo  a  T-shaped  division,  the  two  branches 
then  running  parallel  to  the  surface  of  the  cerebellum  in  a  plane 
vertical  to  that  of  the  dendrites  of  the  cells  of  Purkinje.  Large 
numbers  of  these  T-shaped  neuraxes  produce  the  striation  of  the 
molecular  layer  of  the  cerebellum.  It  is  very  probable  that  during 
their  course  these  parallel  fibers  come  in  contact  with  the  dendrites 
of  the  cells  of  Purkinje.  The  large  stellate  cells  are  fewer  in 
number  and  lie  close  to  the  molecular  layer,  some  of  them  even 
within  this  layer.  Their  dendrites  branch  in  all  directions,  but 
extend  principally  into  the  molecular  layer.  Their  short  neuraxes 
give  off  numerous  collaterals  which  end  in  telodendria  among  the 
granular  cells. 

The  medullary  substance  is  composed  of  the  centrifugal  neu- 
raxes of  the  cells  of  Purkinje  and  of  two  types  of  centripetal  neu- 
raxes, the  mossy  and  the  climbing  fibers.  The  position  of  their 
corresponding  nerve-cells  is  not  definitely  known.  The  mossy 
fibers  branch  in  the  granular  layer  into  numerous  twigs,  and  are 
not  uniform  in  diameter,  but  are  provided  at  different  points  with 
typical  nodular  swellings.  These  fibers  do  not  extend  beyond  the 
granular  layer.  The  climbing  fibers  pass  horizontally  through  the 
granular  layer,  giving  off  in  their  course  numbers  of  collaterals, 
which  extend  to  the  cells  of  Purkinje,  up  the  dendrites  of  which 
they  seem  to  climb. 

In  the  medullary  portion  of  the  cerebellum  are  found  a  number 
of  groups  of  ganglion  cells  known  as  central  gray  nuclei.  The 
nerve-cells  of  these  nuclei  are  multipolar,  with  numerous,  oft- 
branching  dendrites  and  a  single  neuraxis. 


C  THE  CEREBRAL  CORTEX. 

The  cell-bodies  of  the  neurones  of  the  cerebrum  are  grouped  in 
a  thin  layer  of  gray  matter,  varying  in  thickness  from  2  to  4  mm., 
— which,  as  a  continuous  sheet,  completely  covers  the  white  matter 
of  the  hemispheres, — and  in  larger  and  smaller  masses  of  gray  mat- 
ter, known  as  basal  nuclei.  In  our  account  of  the  histologic  struc- 
ture of  the  cerebral  hemispheres  we  shall  confine  ourselves  in  the 
main  to  a  consideration  of  the  cerebral  cortex,  the  thin  layer  of 
gray  matter  investing  the  white  matter. 


376  THE    CENTRAL    NERVOUS    SYSTEM. 

From  without  inward  the  following  layers  may  be  differentiated 
in  the  cerebral  cortex  :  (i)  a  molecular  layer  ;  (2)  a  layer  of  small 
pyramidal  cells  ;  (3)  a  layer  of  large  pyramidal  cells  ;  (4)  a  layer 
of  polymorphous  cells  ;  and  (5)  medullary  substance  or  underlying 
nerve-fibers. 

Aside  from  neurogliar  tissue,  we  find  in  the  molecular  layer  a 
large  number  of  nerve-fibers,  which  cross  one  another  in  all  direc- 
tions, but,  as  a  whole,  have  a  direction  parallel  with  the  surface  of 
the  brain.  Within  this  layer  there  are  found  :  (i)  the  tuft-like  telo- 
dendria  of  the  chief  dendritic  processes  of  the  pyramidal  cells  ;  (2) 
the  terminations  of  the  ascending  neuraxes,  arising  mostly  from  the 
polymorphous  cells  ;  and  (3)  autochthonous  fibers— i.  e.,  those  which 
arise  from  the  cells  of  the  molecular  layer  and  terminate  in  this 
layer.  The  cells  of  the  molecular  layer  may  be  classed  in  three 
general  types — polygonal  cells,  spindle-shaped  cells,  and  triangular 
or  stellate  cells.  The  polygonal  cells  have  from  four  to  six  den- 
drites,  which  branch  out  into  the  molecular  layer  and  may  even 
penetrate  into  the  underlying  layer  of  small  pyramidal  cells.  Their 
neuraxes  originate  either  from  the  bodies  of  the  cells  or  from  one 
of  their  dendrites,  and  take  a  horizontal  or  an  oblique  direction, 
giving  off  in  their  course  a  large  number  of  branching  collaterals, 
which  terminate  in  knob-like  thickenings.  The  spindle=shaped 
cells  give  off  from  their  long  pointed  ends  dendrites  which  extend 
for  some  distance  parallel  with  the  surface  of  the  brain.  These 
branch,  their  offshoots  leaving  them  at  nearly  right  angles,  the 
majority  passing  upward,  assuming  as  they  go  the  characteristics 
of  neuraxes  having  collaterals.  The  arborization  is  entirely  within 
the  molecular  layer.  The  triangular  or  stellate  cells  are  similar 
to  those  just  described,  but  possess  not  two,  but  three,  dendrites. 
The  triangular  and  spindle-shaped  cells,  with  their  numerous  den- 
dritic processes  resembling  neuraxes,  are  characteristic  of  the  cere- 
bral cortex. 

The  elements  which  are  peculiar  to  the  second  and  third  layers 
of  the  cerebral  cortex  are  the  small  (about  10  p.  in  diameter)  and 
large  pyramidal  cells  (from  20  p  to  30  //  in  diameter).  They  are 
composed  of  a  triangular  body,  the  base  of  the  triangle  being  down- 
ward and  parallel  to  the  surface  of  the  brain,  of  a  chief,  principal,  or 
primordial  dendrite  ascending  toward  the  brain-surface,  of  several 
basilar  dendrites  arising  from  the  basal  surface  of  the  cell-body,  and 
of  a  neuraxis  which  passes  toward  the  medullary  substance  and 
which  has  its  origin  either  from  the  base  of  the  cell  or  from  one  of 
the  basilar  dendrites.  The  ascending  or  chief  dendrite  gives  off  a 
number  of  lateral  offshoots  which  branch  freely  and  end  in  terminal 
filaments.  The  main  stem  of  the  dendrite  extends  upward  to  the 
molecular  layer,  in  which  its  final  branches  spread  out  in  the  form 
of  a  tuft.  The  neuraxis,  during  its  course  to  the  white  substance, 
gives  off  in  the  gray  substance  from  six  to  twelve  collaterals,  which 
divide  two  or  three  times  before  terminating. 


THE    CEREBRAL    CORTEX. 


377 


Aside  from  the  fact  that  the  layer  of  polymorphous  cells  con- 
tains a  few  large  pyramidal  cells,  it  consists  principally  of  (i)  mul- 
tipolar  cells  with  short  neuraxes  (Golgi's  cells)  and  (2)  of  cells  with 
only  slightly  branched  dendrites  and  with  neuraxes  passing  toward 
the  surface  of  the  brain  (Martinotti's  cells).  Both  these  types  of  cells 
are,  however,  not  found  exclusively  in  the  layer  of  polymorphous 
cells,  but  may  be  met  with  here  and  there  in  the  layers  of  the  small 
and  large  pyramidal  cells.  The  dendrites  of  the  cells  of  Golgi  are 


Molecular 
layer. 


Layer  of 
large  pyr- 
amidal 
cells. 


_  Medullary 
substance. 


Fig.  312. — Schematic  diagram  of  the 
cerebral  cortex,  after  Golgi  and  Ram6n  y 
Cajal. 


Brush-like 

teloden- 

drion. 


Main  den-  -  - 
drite. 


Secondary 
dendrite. 


Layer  of 
polymer-  B      l  d 

ffita!"  drite' 


Neuraxis 
with  col- 
laterals. 


Fig.  313. — Large  pyramidal  cell  from 
the  human  cerebral  cortex.     Chrome-silver 

method ;  x  l  So- 


projected  in  all  directions,  those  in  the  neighborhood  of  the  medul- 
lary substance  even  penetrating  into  this  layer.  The  neuraxes 
break  up  into  numerous  collaterals,  the  telodendria  of  which  lie  ad- 
jacent to  the  neighboring  ganglion  cells.  The  cells  of  Martinotti, 
which,  as  we  have  seen,  occur  also  in  the  second  and  third  layers, 
are  either  triangular  or  spindle-shaped.  The  neuraxis  of  each  cell 
originates  either  from  the  cell-body  or  from  one  of  its  dendrites,  and 


3/8 


THE    CENTRAL    NERVOUS    SYSTEM. 


ascends  (giving  off  collaterals)  to  the  molecular  layer,  in  which  it 
finally  divides  into  two  or  three  main  branches  ending  in  telo- 
dendria.  Occasionally  it  divides  in  a  similar  manner  in  the  layer 
of  small  pyramidal  cells. 

In  the  medullary  substance  the  following  four  classes  of  fibers 
are  recognized  :  (i)  The  projection  fibers  (centrifugal) — i.  e.,  those 
which  indirectly  connect  the  elements  of  the  cerebral  cortex  with  the 
periphery  of  the  body  ;  their  course  may  or  may  not  be  interrupted 
during  their  passage  through  the  basal  nuclei  ;  (2)  the  commissural 

fibers,  which,  according  to 
the  original  definition,  pass 
through  the  corpus  callo- 
sum  and  anterior  commis- 
sure, thus  joining  corre- 
sponding parts  of  the  two 
hemispheres  ;  (3)  the  asso- 
ciation fibers,  which  con- 
nect different  parts  of  the 
gray  substance  of  the  same 
hemispheres ;  and  (4)  the 
centripetal  or  terminal 
fibers  —  i.  e.,  the  terminal 
arborizations  of  those  neu- 
raxes,  the  cells  of  which 
lie  in  some  other  region  of 
the  same  or  opposite  hemi- 
sphere, or  even  in  some 
more  distant  portion  of  the 
nervous  system.  The  pro- 
jection fibers  originate  from 
the  pyramidal  cells,  some 
of  them  perhaps  from  the 
polymorphous  cells.  The 
commissural  fibers  are  also 


Fig.  314. — Schematic  diagram  of  the  cerebral 
cortex  :  a,  Molecular  layer  with  superficial  (tan- 
gential) fibers  ;  b,  striation  of  Bechtereff-Kaes  ;  c, 
layer  of  small  pyramidal  cells  ;  d,  stripe  of  Bail- 
larger;  e,  radial  bundles  of  the  medullary  sub- 
stance ;  f,  layer  of  polymorphous  cells. 


derived  from  the  pyramidal 
cells,  and  lie  somewhat 
deeper  in  the  white  sub- 
stance than  the  association 
fibers.  With  the  exception 
of  those  which  join  the 

cunei  and  those  which  lie  in  the  anterior  commissure,  all  the 
commissural  fibers  are  situated  in  the  corpus  callosum.  They 
give  off  during  their  passage  through  the  hemispheres  large  num- 
bers of  collaterals,  which  penetrate  at  various  points  into  the  gray 
substance  and  end  there  in  terminal  filaments.  In  this  respect 
their  arborization  is  contrary  to  the  old  definition  of  these  fibers,  and 
the  latter  must  be  completed  by  the  statement  that,  besides  joining 
symmetric  points  of  the  two  hemispheres,  they  also,  by  means  of 


THE    OLFACTORY    BULB.  3/9 

their  collaterals,  may  connect  other  areas  of  the  gray  substance 
with  the  peripheral  regions  supplied  by  their  end-tufts  (Ramon  y 
Cajal,  93).  The  association  fibers  have  their  origin  also  in  the 
pyramidal  cells.  In  the  medullary  substance  their  neuraxes  divide 
T-shaped,  and  after  a  longer  or  shorter  course  penetrate  into  the 
gray  substance  of  the  same  hemisphere,  where  they  end  as  ter- 
minal fibers.  A  few  collaterals  are,  however,  previously  given  off, 
which  also  terminate  in  the  same  manner  in  the  gray  substance. 
The  association  fibers  form  the  bulk  of  the  medullary  rays. 

On  examining  a  vertical  section  through  one  of  the  cerebral 
convolutions  a  number  of  successive  filiations  may  be  seen.  These 
are  more  or  less  distinct,  according  to  the  region,  and  consist  of 
strands  of  medullated  nerve-fibers  between  the  layers  of  cells,  and 
parallel  with  the  surface  of  the  convolution.  The  most  superficial 
form  a  layer  of  tangential  fibers.  Between  the  molecular  layer  and 
the  layer  of  small  pyramidal  cells  is  the  striation  of  Bechtereff  and 
Kaes,  and  in  the  region  of  the  large  pyramidal  cells  the  striation  of 
Baillarger  (Gennari)  corresponding  to  the  striation  of  Vicq  d'Azyr 
in  the  cuneus.  In  figure  314  the  medullary  substance  is  seen 
below,  with  rays,  composed  of  parallel  bundles  of  fibers,  passing 
upward  into  the  gray  substance  ;  in  reality  these  fibers  penetrate 
much  higher  than  is  shown  in  the  illustration. 


D.  THE  OLFACTORY  BULB. 

The  olfactory  bulb  is  composed  of  five  layers,  which  are  espe- 
cially well  marked  on  its  ventral  side  :  first,  the  layer  of  peripheral 
nerve-fibers  ;  second,  the  layer  of  olfactory  glomeruli  ;  third,  the 
stratum  gelatinosum,  or  molecular  layer  ;  fourth,  the  layer  of  pyr- 
amidal cells  (mitral  cells)  ;  and,  fifth,  the  granular  layer  with  the 
deeper  nerve-fibers. 

The  layer  of  peripheral  fibers  is  composed  of  the  nerve- 
bundles  of  the  olfactory  nerve  which  cross  one  another  in  various 
directions  and  form  a  nerve-plexus.  The  glomerular  layer  con- 
tains peculiar,  regularly  arranged,  round  or  oval,  and  sharply  defined 
structures,  which  were  first  accurately  studied  by  Golgi.  They  are 
known  as  glomeruli  (from  100  fj.  to  300  p.  in  diameter),  and  are  in 
reality  complexes  of  intertwining  telodendria.  As  we  shall  see, 
the  epithelial  cells  of  the  olfactory  region  of  the  nose  must  be 
regarded  as  peripheral  ganglion  cells  and  their  centripetal  (basal) 
processes  as  neuraxes.  The  telodendria  of  these  neuraxes,  together 
with  those  of  the  dendrites  from  the  mitral  or  other  cells,  come  in 
contact  with  each  other  within  the  olfactory  glomeruli.  The  molec- 
ular layer  consists  of  small,  spindle-shaped  ganglion  cells.  Their 
neuraxes  enter  the  fifth  layer  and  their  short  dendrites  end  in  ter- 
minal ramifications  in  the  glomeruli.  The  mitral  cells  give  off 
neuraxes  from  their  dorsal  surfaces  which  also  enter  the  granular 


380 


THE    CENTRAL    NERVOUS    SYSTEM. 


layer,  but  the  majority  of  their  dendrites  break  up  into  terminal 
ramifications  in  the  olfactory  glomeruli,  as  just  described.  The 
granular  layer  (absent  in  the  illustration)  is  made  up  of  nerve-cells 
and  nerve-fibers  ;  but,  aside  from  these,  we  find  also  large  numbers 
of  peculiar  cells  with  a  long  peripherally  and  several  short  centrally 
directed  dendrites.  No  neuraxes  can  be  demonstrated  in  these 
cells  (granular  cells).  This  layer  also  contains  the  stellate  ganglion 
cells.  The  latter  are  not  numerous,  but  lie  scattered,  and  each  pos- 
sesses several  short  dendrites  and  a  peripherally  directed  neuraxis 
which  ends  in  the  molecular  layer  in  a  rich  arborization.  The  deep 
nerve-fibers  are  grouped  into  bundles  which  inclose  between  them 
the  granular  and  stellate  cells  just  mentioned.  These  nerve-fibers 


Mitral  cells. 


Molecu- 
lar layer. 


Layer  of  olfactory 
glomeruli. 


Peripheral  nerve- 
fibers. 


Fig-  3i5- — The  olfactory  bulb,  after  Golgi  and  Ram6n  y  Cajal.     The  granular  layer  is 

not  shown. 

are  derived  partly  from  the  neuraxes  of  the  pyramidal  or  mitral  cells 
and  partly  from  the  cells  of  the  molecular  layer,  while  some  of 
them  are  centripetal  fibers  from  the  periphery,  which  end  between 
the  granules  of  the  fifth  layer. 

E.  EPIPHYSIS  AND  HYPOPHYSIS. 

In  mammalia  the  epiphysis,  or  pineal  gland,  consists  of  a 
fibrous  capsule  derived  from  the  pia  mater,  from  which  numerous 
fibrous  tissue  septa  and  processes  pass  into  the  gland,  uniting  to 
form  quite  regular  round  or  oval  compartments  in  which  closed 
follicles  or  alveoli,  whose  walls  cpnsist  of  epithelial  cells,  are  found. 


EPIPHYSIS    AND    HYPOPHYSIS.  381 

The  epithelial  cells  forming  the  walls  of  the  follicles  are  of  cubic  or 
short  columnar  shape,  and  may  be  arranged  in  a  single  layer  or 
may  be  pseudostratified  or  stratified.  Follicles  completely  filled  with 
cellular  elements  are  found.  Other  follicles  contain  peculiar  con- 
cretions, known  as  brain-sand  or  acervulus,  of  irregular  round  or 
oval  or  mulberry  shape.  Medullated  nerve-fibers  have  been  traced 
into  the  epiphysis,  but  their  mode  of  termination  is  not  known. 

The  hypophysis,  or  pituitary  body,  consists  of  two  lobes. 
The  posterior  or  infundibular  lobe  is  developed  from  the  floor  of 
the  first  primary  brain-vesicle,  and  remains  attached  to  the  floor  of 
the  third  ventricle  by  a  stalk,  known  as  the  infundibulum  ;  the 
anterior  or  glandular  lobe  develops  from  a  bud  derived  from  the 
primary  oral  ectoderm,  known  as  Rathke's  pouch.  The  distal  end 
of  this  pouch  comes  in  contact  with  the  anterior  surface  of  the 
lower  portion  of  the  infundibulum,  and  becomes  loosely  attached 
to  it.  As  the  bones  at  the  base  of  the  skull  develop,  the  attenuated 
oral  end  of  Rathke's  pouch  atrophies,  the  distal  end  becoming 
finally  completely  severed  from  the  buccal  cavity. 

In  the  infundibular  lobe  of  the  hypophysis  of  the  dog,  Berkley 
(94)  described  three  portions  presenting  different  microscopic  struc- 
ture. His  account  will  here  be  followed  :  (i)  An  outer  stratum 
consisting  of  three  or  four  layers  of  cells  resembling  ependymal 
cells,  which  are  separated  into  groups  by  thin  strands  of  fibrous 
tissue  entering  from  the  fibrous  covering  of  this  lobe.  (2)  A  zone 
consisting  of  glandular  epithelial  cells  which  in  certain  places  are 
arranged  in  the  form  of  alveoli,  often  containing  a  colloid  substance. 
This  zone  merges  into  the  central  portion,  (3),  containing  variously 
shaped  cells  and  connective-tissue  partitions  with  blood-vessels.  In 
this  portion  neurogliar  cells  (see  these)  and  nerve-cells  were  stained 
by  the  chrome-silver  method. 

The  glandular  or  anterior  lobe  resembles  slightly  in  structure 
the  parathyroid.  This  lobe  is  surrounded  by  a  fibrous  tissue  capsule 
and  within  it  are  found  variously  shaped  alveoli  or  follicles,  or, 
again,  columns  or  trabeculae  of  cells  separated  by  a  very  vascular 
connective  tissue.  In  the  alveoli  or  columns  of  cells  are  found  two 
varieties  of  glandular  cells,  which  may  be  differentiated  more  by 
their  staining  reaction  than  by  their  size  and  structure,  although 
they  present  slight  structural  differences.  One  variety  of  cells  pos- 
sesses a  protoplasm  which  shows  affinity  for  acid  stains  ;  these  are 
known  as  chromophilic  cells.  They  are  of  nearly  round  or  oval 
shape,  with  nuclei  centrally  placed,  and  have  a  protoplasm  present- 
ing coarse  granules.  The  other  variety  of  cells,  known  as  chief 
cells,  are  more  numerous  than  the  chromophilic.  They  are  of  cubic 
or  short  columnar  shape,  with  nuclei  placed  in  the  basal  portions 
of  the  cells  and  with  protoplasm  showing  a  fine  granulation  and 
with  an  affinity  for  basic  stains.  Now  and  then  alveoli  containing 
a  colloid  substance,  similar  to  that  found  in  the  alveoli  of  the  thy- 
roid gland,  may  be  observed.  The  blood-vessels  of  the  glandular 


382  THE    CENTRAL    NERVOUS    SYSTEM. 

portion  are  relatively  large,  the  majority  of  them  having  only  an 
endothelial  lining.  In  the  glandular  portion  of  the  hypophysis  of 
the  dog,  Berkley  (94)  found  small  varicose  nerve-fibers  belonging  to 
the  sympathetic  system.  From  the  larger  bundles,  which  follow 
the  blood-vessels,  are  given  off  single  fibers  or  small  bundles  of 
such,  which  end  on  the  glandular  elements  in  numerous  small 
nodules. 

F.  GANGLIA. 

In  the  course  of  peripheral  nerves  are  found  numerous  larger  and 
smaller  groups  of  nerve-cells,  known  as  ganglia.  The  neurones  of 
these  ganglia  are  in  intimate  relation  with  the  neurones  of  the  cen- 


Fig.  316. — Longitudinal  section  of  spinal  ganglion  of  cat. 

tral  nervous  system,  and  may,  therefore,  be  discussed  with  the  lat- 
ter. According  to  the  structure  and  function  of  their  neurones,  the 
ganglia  are  divided  into  two  groups — (i)  spinal  or  sensory  ganglia 
and  (2)  sympathetic  ganglia. 

The  spinal  ganglia  are  situated  on  the  posterior  roots  of  the 
spinal  nerves.  Certain  cranial  ganglia — namely,  the  Gasserian, 
geniculate,  and  auditory  ganglia,  the  jugular  and  petrosal  gan- 
glia of  the  glossopharyngeal  nerves,  and  the  root  and  trunk  ganglia 
of  the  vagi — are  classed  with  the  spinal  ganglia,  since  they  present 
the  same  structure.  The  spinal  and  sensory  cranial  ganglia  are 
surrounded  by  firm  connective-tissue  capsules,  continuous  with  the 
perineural  sheaths  of  the  incoming  and  outgoing  nerve-roots.  From 


GANGLIA.  383 

these  capsules  connective-tissue  septa  and  trabeculae  pass  into 
the  interior  of  the  ganglia,  giving  support  to  the  nerve-elements. 
The  cell-bodies  (ganglion  cells)  of  the  neurones  constituting  these 
ganglia  are  arranged  in  layers  under  the  capsule  and  in  rows  and 
groups  or  clusters  between  the  nerve-fibers  in  the  interior  of  the 
ganglia.  More  recent  investigations  have  shown  that  several  types 
of  neurones  are  to  be  found  in  the  spinal  and  cranial  sensory  gan- 
glia ;  of  these,  we  may  mention  the  following:  (i)  Large  and 
small  unipolar  cells  with  T-  or  Y-shaped  division  of  the  process. 
These  neurones,  which  constitute  the  greater  number  of  all  the 
neurones  of  the  ganglia  under  discussion,  consist  of  a  round  or 
oval  cell-body,  from  which  arises  by  means  of  an  implantation  cone 


Fig.  317. — Ganglion  cell  from  the  Gasserian  ganglion  of  a  rabbit;  stained  in  methylene- 

blue  (infra  vitani}. 

a  single  process,  which,  soon  after  it  leaves  the  cell,  becomes  in- 
vested with  a  medullary  sheath  and  usually  makes  a  variable  num- 
ber of  spiral  turns  near  the  cell-body.  According  to  Dogiel,  this 
process  divides  into  two  branches,  usually  at  the  second  or  third 
node  of  Ranvier,  sometimes  not  until  the  seventh  node  is  reached. 
Of  these  two  branches,  the  peripheral  is  the  larger,  and  enters  a 
peripheral  nerve-trunk  as  a  medullated  sensory  nerve-fiber,  termi- 
nating in  one  of  the  peripheral  sensory  nerve-endings  previously 
described.  The  central  process,  the  smaller  of  the  two,  becomes  a 
medullated  nerve-fiber,  which  enters  the  spinal  cord  or  medulla  in  a 
manner  described  in  a  former  section.  The  cell-body  of  each  of 
these  neurones  is  surrounded  by  a  nucleated  capsule,  continuous  with 


384  THE    CENTRAL    NERVOUS    SYSTEM. 

the  neurilemma  of  the  single  process.  (2)  Type  II  spinal  ganglion 
cell  of  Dogiel.  Dogiel  has  recently  described  a  second  type  of  spinal 
ganglion  cell  which  differs  materially  from  the  type  just  described. 
The  cell-bodies  of  these  neurones  resemble  closely  those  of  the  typ- 
ical spinal  ganglion  neurones.  Their  single  medullated  processes 
divide,  however,  soon  after  leaving  the  cells  into  branches  which 
divide' further  and  which  do  not  pass  beyond  the  bounds  of  the  gan- 
glia but  terminate,  after  losing  their  medullary  sheaths,  in  compli- 
cated pericapsular  and  pericellular  end-plexuses  surrounding  the 
capsules  and  cell-bodies  of  the  typical  spinal  ganglion  cells.  (3)  Mul- 
tipolar  ganglion  cells  ;  in  nearly  all  spinal  and  cranial  ganglia  there 
are  found  a  few  multipolar  nerve-cells,  which  in  shape  and  struc- 
ture resemble  the  nerve-cells  of  the  sympathetic  system. 


Fig.  318. — Diagram  showing  the  relations  of  the  neurones  of  a  spinal  ganglion; 
/.  r.,  posterior  root;  a.  r.,  anterior  root;  /.  s.,  posterior  branch  and  a.  s.,  anterior 
branch  of  spinal  nerve  ;  w.  r.,  white  ramus  communicans  ;  a,  large,  and  b,  small  spinal 
ganglion  cells  with  T-shaped  division  of  process  ;  c,  type  II  spinal  ganglion  cells  (Dogiel); 
s,  multipolar  cell ;  d,  nerve-fiber  from  sympathetic  ganglion  terminating  in  pericellular 
plexuses  (slightly  modified  from  diagram  given  by  Dogiel). 


Entering  the  spinal  ganglia  from  the  periphery  are  found  a  rel- 
atively small  number  of  small,  medullated  or  nonmedullated  nerve- 
fibers,  probably  derived  from  sympathetic  ganglia.  These  nerve- 
fibers,  medullated  and  nonmedullated,  the  former  losing  their 
medullary  sheaths  within  the  ganglia,  approach  a  spinal  ganglion 
cell,  and  after  making  a  few  spiral  turns  about  its  process,  termi- 
nate in  pericapsular  and  pericellular  end-plexuses.  Dogiel  believes 
that  the  cell-bodies  and  capsules  thus  surrounded  by  the  terminal 
branches  of  the  sympathetic  fibers  terminating  in  the  spinal  ganglia 
belong  to  the  spinal  ganglion  cells  of  the  second  type  first  described 
by  him.  In  figure  318  is  represented  by  way  of  diagram  the 
structure  of  a  spinal  ganglion. 

In  the  medium-sized  cells  (from  30  //  to  45  p.  in  diameter)  of  the 


GANGLIA. 


spinal  ganglia  of  the  frog,  von  Lenhossek  (95)  found  centrosomes 
surrounded  by  a  clear  substance  (centrospheres).  The  entire  struc- 
ture lay  in  a  depression  of  the  nucleus  and  contained  more  than 
twelve  extremely  minute  granules  (centrosomes),  which  showed  a 
staining  reaction  different  from  that  of  the  numerous  concentrically 
laminated  granules  present  in  the  protoplasm.  This  observation  is 
interesting  in  that  it  proves  that  centrosome  and  sphere  occur  also 
in  the  protoplasm  of  cells  which  have  not  for  a  long  time  under- 
gone division  and  in  which  there  is  no  prospect  of  future  division. 

Sympathetic  Ganglia. — The  ganglia  of  the  sympathetic  ner- 
vous system  comprise  those  of  the  two  great  ganglionated  cords, 
found  on  each  side  of  the  vertebral  column  and  extending  from  its 
cephalic  to  its  caudal  end,  with  which  may  be  grouped  certain  cranial 
ganglia  having  the  same  structure, — namely,  the  sphenopalatine, 
otic,  ciliary,  sublingual,  and  submaxillary  ganglia ;  also  three  un- 


Fig.  319. — Neurone  from  inferior  cervical  sympathetic  ganglion  of  a  rabbit;  methylene- 

blue  stain. 


paired  aggregations  of  ganglia,  found  in  front  of  the  spinal  column, 
of  which  the  cardiac  is  in  the  thorax,  the  semilunar  in  the  abdomen, 
and  the  hypogastric  in  the  pelvis  ;  and  further,  large  numbers  of 
smaller  ganglia,  the  greater  number  of  which  are  of  microscopic 
size  and  are  found  in  the  walls  of  the  intestinal  canal  and  bladder, 
in  the  respiratory  passages,  in  the  heart,  and  in  or  near  the  majority 
of  the  glands  of  the  body. 

The  sympathetic  ganglia  are  inclosed  in  fibrous  tissue  capsules 
continuous  with  the  perineural  sheaths  of  their  nerve-roots.  The 
thickness  of  the  capsule  bears  relation  to  the  size  of  the  ganglion, 
being  thicker  in  the  larger  and  thinner  in  the  smaller  ones.  From 
these  capsules  thin  connective-tissue  septa  or  processes  pass  into 
the  interior  of  the  ganglia,  supporting  the  nerve  elements. 

The  sympathetic  neurones,  the  cell-bodies  and  dendritic  processes 
of  which  are  grouped  to  form  the  sympathetic  ganglia,  are  variously 
25 


386  THE    CENTRAL    NERVOUS    SYSTEM. 

shaped  unipolar,  bipolar,  and  multipolar  cells,  the  cell-bodies  of 
which  are  surrounded  by  nucleated  capsules,  continuous  with  the 
neurilemma  of  their  neuraxes.  In  the  sympathetic  ganglia  of  mam- 
malia and  birds  the  great  majority  of  sympathetic  neurones  are 
multipolar,  although  in  nearly  all  ganglia  a  small  number  of  bipolar 
and  unipolar  cells  are  to  be  found,  usually  near  the  poles  of  the 
ganglia. 

The  dendrites  of  the  sympathetic  neurones  in  any  one  ganglion 
branch  repeatedly.  Of  these  branches,  some  extend  to  the  per- 
iphery of  the  ganglion,  where  they  interlace  to  form  a  peripheral 
subcapsular  plexus,  while  others  interlace  to  form  plexuses  between 
the  cell-bodies  of  the  neurones  in  the  interior  of  the  ganglion — 
pericellular  plexuses.  These  pericellular  plexuses  are  external  to 
the  capsules  surrounding  the  cell-bodies  of  the  sympathetic  neurones. 


Fig.  320. — From  section  of  semilunar  ganglion  of  cat ;  stained  in  methyl ene-blue,  infra 
vitam  (Huber,  Journal  of  Morphology,  1899). 

The  neuraxes  of  the  sympathetic  neurones,  the  majority  of 
which  are  nonmedullated,  the  remainder  surrounded  by  delicate 
medullary  sheaths,  arise  from  the  cell-bodies  either  from  implanta- 
tion cones  or  from  dendrites  at  variable  distances  from  the  cell- 
bodies,  leave  the  ganglion  by  way  of  one  of  its  nerve-roots,  and 
terminate  in  heart  muscle  tissue,  nonstriated  muscle,  and  glandular 
tissue,  and  to  some  extent  in  other  ganglia,  both  sympathetic  and 
spinal.  Terminating  in  all  sympathetic  ganglia  are  found  certain 
small  medullated  nerve-fibers,  varying  in  size  from  about  1.5  //  to 
3  fjL.  The  researches  of  Gaskell,  Langley,  and  Sherrington  have 
shown  that  these  small  medullated  nerve-fibers  leave  the  spinal 
cord  through  the  anterior  roots  of  the  spinal  nerves  from  the  first 
dorsal  to  the  third  or  fourth  lumbar  and  reach  the  sympathetic 


GANGLIA. 


ganglia  through  the  white  rami  communicantes.  Similar  small 
medullated  nerve-fibers  are  found  in  certain  cranial  nerves.  These 
small  medullated  nerve-fibers,  which  may  be  spoken  of  as  white 
rami  fibers,  after  a  longer  or  shorter  course,  in  which  they  may 
pass  through  one  or  several  ganglia  without  making  special  con- 
nection with  the  neurones  contained  therein,  terminate  in  some 
sympathetic  ganglion  in  a  very  characteristic  manner.  After  enter- 
ing the  sympathetic  ganglion  in  which  they  terminate,  they  branch 
repeatedly  while  yet  medullated.  The  resulting  branches  then  lose 
their  medullary  sheaths  and  divide  into  numerous  small,  varicose 
nerve-fibers,  which  interlace  to  form  intracapsular  plexuses,  which 
surround  the  cell-bodies  of  the  sympathetic  neurones.  In  the 
sympathetic  ganglia  of  mammalia  such  intracapsular  pericellular 


Fig.  321. — From  section  of  stellate  ganglion  of  dog,  stained  in  methylene-blue  and  alum 
carmin  :  a,  white  ramus  fiber  (Huber,  Journal  of  Morphology,  1899). 

plexuses  may  be  very  simple,  consisting  of  only  a  few  varicose 
nerve-fibers,  or  very  complicated,  consisting  of  many  such  fibers. 
In  the  sympathetic  ganglia  of  reptilia,  in  which  are  found  very 
large  sympathetic  neurones,  the  white  rami  fibers  are  wound  spirally 
about  the  cell-bodies  of  such  neurones  before  terminating  in  com- 
plicated pericellular  plexuses.  In  the  frog  and  other  amphibia  the 
sympathetic  neurones  are  unipolar  nerve-cells.  The  white  rami 
fibers  terminating  in  the  sympathetic  ganglia  of  amphibia  are  wound 
spirally  about  the  single  processes  of  these  unipolar  cells  while  yet 
medullated  fibers,  but  they  lose  their  medullary  sheaths  before  ter- 
minating in  the  intracapsular  pericellular  plexuses.  From  what 
has  been  said  concerning  the  white  rami  fibers  and  their  relation  to 
the  sympathetic  neurones,  it  is  evident  that  the  sympathetic  neu- 


388  THE    CENTRAL    NERVOUS    SYSTEM. 

rones,  the  cell-bodies  and  dendrites  of  which  are  grouped  to  form 
the  sympathetic  ganglia,  form  terminal  links  in  nerve  or  neurone 
chains  ;  the  second  link  of  these  chains  is  formed  by  neurones  the 
cell-bodies  of  which  are  situated  in  the  spinal  cord  or  medulla,  the 


Fig.  322. — From  section  of  sympathetic  ganglion  of  turtle,  showing  white  rami 
fibers  wound  spirally  about  a  large  process  of  a  unipolar  cell,  and  ending  in  pericellular 
plexus  (Huber,  Journal  of  Morphology,  1899). 

neuraxes  leaving  the  cerebrospinal  axis  through  the  white  rami  as 
small  medullated  nerve-fibers,  which  terminate  in  pericellular  plex- 
uses inclosing  the  cell-bodies  of  the  sympathetic  neurones. 

Large  medullated  nerve-fibers,  the  dendrites  of  spinal  ganglion 
neurones,  reach  the  sympathetic  ganglia  through  the  white  rami. 


Fig.  323. — From  section  of  sympathetic  ganglion  of  frog,  showing  spiral  fiber  (white  ramus 
fiber)  and  pericellular  plexus  (Huber,  Journal  of  Morphology,  1899). 

They  make,  however,  no  connection  with  the  sympathetic  neurones, 
but  pass  through  the  ganglia  to  reach  the  viscera,  where  they  ter- 
minate in  special  sensory  nerve-endings  or  in  free  sensory  nerve- 
endings. 


RELATIONSHIP    OF    NEURONES.  389 


G.  GENERAL   SURVEY  OF  THE  RELATIONS   OF  THE 

NEURONES  TO  ONE  ANOTHER  IN  THE 

CENTRAL  NERVOUS  SYSTEM. 

The  following  figures  illustrate  the  modern  theories  with  re- 
gard to  the  relationship  of  the  neurones  in  a  sensorimotor  reflex 
cycle.  The  pathway  along  which  the  impulse  from  the  stimulated 
area  of  the  body  is  transmitted  to  the  motor  nerve  end-organ  tra- 
verses two  neurones  (primary  neurones)  which  are  in  contact  by 
means  of  their  telodendria  situated  within  the  gray  matter  of  the 
spinal  cord.  The  cell-body  of  the  sensory  neurone  lies  within  the 
spinal  ganglion  ;  that  of  the  motor  neurone,  in  the  anterior  horn  of 
the  spinal  cord.  The  dendrite  of  the  sensory  neurone  commences 


sJV 


mN  __ 


Fig.  324. — Schematic  diagram  of  a  sensorimotor  reflex  arc  according  to  the  modern 
neurone  theory  ;  transverse  section  of  spinal  cord :  m Ny  Motor  neurone  ;  sA\  sensory 
neurone  ;  C1,  nerve-cell  of  the  motor  neurone  5  C2,  nerve-cell  of  the  sensory  neurone  ; 
d,  dendrite  ;  «,  neuraxis  of  both  neurones  ;  t;  telodendria  ;  M,  muscle-fiber ;  //,  skin 
with  peripheral  telodendrion  of  sensory  neurone.  • 

as  a  telodendrion  in  the  skin  and  transmits  a  cellulipetal  impulse, 
while  its  cellulifugal  neuraxis  and  telodendrion  (the  latter  in  the 
gray  matter  of  the  cord)  transfer  the  impulse  to  the  cellulipetal 
telodendrion  of  the  motor  neurone.  The  cellulifugal  neuraxis  of  the 
latter  finally  ends  as  a  telodendrion  in  the  muscle.  (Figs.  324 
and  325.) 

In  the  case  of  longer  tracts  the  conditions  are  somewhat  more 
complicated,  as,  for  instance,  in  tracing  the  impulse  along  the  sen- 
sory fibers  to  the  cortex  of  the  brain,  and  from  there  along  the 
motor  fibers  to  the  responding  muscle.  In  such  cases  secondary 
neurones  are  called  into  play  by  means  of  their  telodendria,  which 
are  necessarily  in  contact  with  the  primary  neurones  just  described. 


390 


THE    CENTRAL    NERVOUS    SYSTEM. 


When  we  take  into  consideration  the  simplest  possible  case,  that 
of  the  motor  segment  of  such  a  neurone-chain,  we  find,  for  instance 
(Fig.  326),  that  the  neuraxis  of  a  pyramidal  cell  in  the  brain  cortex 
(psychic  cell)  enters  the  white  substance  and  traverses  it  as  a  nerve- 
fiber  through  the  peduncle  and  the  pyramid  into  the  crossed 
pyramidal  tract  of  the  opposite  side.  Here  its  telodendria  come  in 
contact  with  those  of  the  motor  neurone  of  the  anterior  horn. 

In  the  foregoing  instance  the  motor  nerve  tract  is  composed  of 
two  neurones — of  a  motor  neurone  of  the  first  order,  extending 
from  the  cortex  of  the  brain  to  the  anterior  cornua  of  the  spinal 
cord,  and  of  a  motor  neurone  of  the  second  order,  the  elements 
of  which  extend  from  the  anterior  cornua  to  the  telodendria  in  the 
muscle. 


tiu: 
,  \  Ib^v .  y  : 


slV 


d 


Fig".  325. — Schematic  diagram  of  a  sensorimotor  reflex  cycle ;  sagittal  section  of 
the  spinal  cord:  C1,  Motor  cells  of  the  anterior  cornua;  n,  n,  neuraxes  ;  sN,  sensory 
neurone  ;  C2,  spinal  ganglion  cell ;  C,  collaterals  of  the  sensory  neuraxes  ;  </,  dendrite  of 
sensory  neurone  ;  the  broken  lines  at  the  cells  on  the  left  indicate  their  dendrites. 


The  sensory  tract  may  likewise  be  composed  of  neurones  of  the 
first  and  second  orders.  The  cellulifugal  neuraxis  arising  from  a 
cell  of  the  spinal  ganglion  passes  to  the  posterior  column  of  the 
cord,  gives  off  collaterals  to  the  latter,  and  then  passes  upward  by 
means  of  its  ascending  branch  through  the  posterior  column  to  the 
medulla.  Although  here  the  relationship  is  not  so  clearly  defined 
as  in  the  motor  tract,  it  may  nevertheless  be  assumed  that  the  cellu- 
lifugal (but  centripetally  conducting)  neuraxis  at  some  point  or 
other  terminates  in  telodendria  (sensory  neurone  of  the  first  order), 
which  enter  into  contact  with  the  corresponding  structures  of  a  cell 
of  the  spinal  cord  or  medulla  oblongata.  These  cells  would  then 


RELATIONSHIP    OF    NEURONES. 


391 


constitute  the  sensory  neurones  of  the  second  order.  Exactly  how 
their  cellulifugal  neuraxes  end  has  not  as  yet  been  fully  determined, 
but  it  is  very  probable  that  in  this  case  the  telodendria  are  repre- 
sented by  the  coarse  end-fibers  which  penetrate  into  the  brain  cor- 
tex, and  here  seem  to  come  in  contact  with  the  dendrites  of  the  pyr- 
amidal cells. 


Fig.  326. — Schematic  diagram  of  the  reflex  tracts  between  a  peripheral  organ  and 
the  brain  cortex  :  H,  Cerebral  cortex  ;  ntN1,  motor  neurone  of  the  first,  sN2,  sensory 
neurone  of  the  second,  degree  ;  Cl,  motor  cell  of  the  spinal  cord  ;  C2,  sensory  cell  of  a 
spinal  ganglion;  C"3,  pyramidal  cell  of  the  brain  cortex  (pyschic  cell)  ;  C*,  nerve-cell 
of  a  sensory  neurone  of  the  second  degree  ;  n,  n,  n,  «,  neuraxes  ;  </,  d^  dendrites  ;  ct  c,  c,  c^ 
collaterals;  /,  /,  telodendria;  sNl,  sensory  neurone  first  degree;  mN^^  motor  neurone 
second  degree. 


392 


THE   CENTRAL    NERVOUS    SYSTEM. 


H.  THE  NEUROGLIA. 


We  may  now  consider  the  neuroglia,  a  tissue  distributed 
throughout  the  central  nervous  system  and  looked  upon  as  a  sup- 
porting tissue.  Its  relation  to  the  other  tissues  has  long  been  a 
matter  of  controversy,  but  modern  observers  have  shown  conclu- 
sively that  the  neuroglia  is  of  ectodermic  origin,  at  least  so  far  as 
its  cellular  elements  are  concerned. 

At  an  early  stage  of  embryonic  development  there  are  seen  in 
the  spinal  cord,  and  also  in  the  brain,  elements  radially  disposed 
around  the  neural  canal,  which  upon  closer  observation  appear 
to  be  processes  emanating  from  the  epithelial  cells  lining  the  neural 
canal.  These  processes  may  undergo  repeated  dichotomous  divi- 
sion, ending  finally  in  a  swelling 
near  the  periphery  of  the  cord. 
These  cells  are  known  as  epen- 
dymal  cells,  and  are  differenti- 
ated from  ectodermal  cells,  called 
spongioblasts.  In  later  stages 
the  radial  arrangement  is  still 
preserved,  but  the  cell-bodies  no 
longer  all  border  upon  the  cen- 
tral canal,  many  being  found  at 
varying  distances  from  the  latter. 
At  this  stage  in  the  development 
of  the  spinal  cord,  the  elements 
retaining  their  original  charac- 
teristics are  situated  only  in  the 
region  of  the  ventral  and  dorsal 
fissures  of  the  spinal  cord,  and 
during  further  development  in- 
crease in  number. 

These    observations     would 
seem  to  indicate  that  at  least  a 

portion  of  the  neurogliar  cells,  which  develop  from  the  eperidymal 
cells  previously  mentioned,  originate  from  the  epithelium  of  the 
central  canal,  and  that  from  here  they  are  gradually  pushed  toward 
the  periphery  of  the  cord.  This  assumption  is  still  further  strength- 
ened by  the  fact  that  later  the  epithelial  cells  of  the  central  canal 
still  continue  to  divide.  Later  observations  (Schaper,  97)  show,  how- 
ever, that  neurogliar  cells  develop  also  from  certain  un differentiated 
germinal  cells  of  the  neuraT  canal,  of  ectodermal  origin,  which 
wander  from  their  position,  near  the.  neural  canal  toward  the  per- 
iphery of  the  medullary  tube,  where  they  develop  into  neurogliar 
cells. 

In  the  adult  the  epithelium  of  the  central  canal  and  that  of  the 
brain  cavities  (the  ependyma)  is  of  the  pseudostratified  variety  with 


Fig-  327- — Neurogliar  cells  :  a,  From 
spinal  cord  of  embryo  cat ;  b,  from  brain  of 
adult  cat :  stained  in  chrome-silver. 


THE    MEMBRANES    OF    THE    CENTRAL    NERVOUS   SYSTEM.          393 

two  or  three  strata  of  nuclei.  The  basilar  processes  of  the  cells 
are  very  long,  may  be  branched,  and,  as  a  rule,  describe  a  tortuous 
course. 

The  shape  and  structure  of  the  neurogliar  cells  (spider-cells)  vary 
somewhat  in  different  parts  of  the  central  nervous  system.  From 
the  bodies  of  these  cells  numerous  delicate  processes  are  sent  out, 
which  in  the  one  variety  of  cell — that  occurring  principally  in  the 
white  matter — do  not  branch.  Similar  cells,  with  shorter  but  occa- 
sionally dividing  processes,  are  situated  for  the  most  part  in  the 
gray  matter.  Other  neurogliar  cells  may  be  distinguished  from  the 
varieties  just  described  by  the  smaller  number  of  their  processes 
and  by  their  correspondingly  larger  bodies. 

A  large  proportion  of  the  fine  fibers  found  in  the  gray  and  the 
white  matter  are  processes  of  the  neurogliar  cells.  Whether  the 
spinal  cord  contains  other  similar  cellular  and  fibrillar  elements  of 
niesodermic  origin  is  an  unsettled  question.  There  seems  to  be  no 
doubt,  however,  that  connective  tissue  (other  than  that  composing 
the  pial  processes)  always  accompanies  the  numerous  blood-vessels 
penetrating  into  the  spinal  cord. 

The  majority  of  investigators  have  described  the  various  fibers 
and  fibrils  brought  to  view  by  certain  methods  as  processes  of  the 
neurogliar  cells.  Weigert  (95)  and  Mallory  have  demonstrated,  by 
means  of  special  methods,  the  existence  of  neuroglia-fibers  in  the 
adult  human  brain  which  are  nowhere  connected  with  cellular  ele- 
ments, although  they  frequently  group  themselves  around  a  cell  as 
an  axis,  and  thus  simulate  with  the  latter  the  "spider-cells"  of 
some  authors.  The  neurogliar  elements  of  the  embryo  and  fetus 
have  as  yet  never  been  demonstrated  by  Weigert's  method,  but 
have,  as  a  rule,  been  studied  by  means  of  Golgi's  method.  Reinke 
(97)  has  very  recently  found  in  the  white  matter  of  the  adult  human 
spinal  cord  neurogliar  cells  with  processes  and  neuroglia-fibers 
having  no  connection  with  cells. 


L  THE  MEMBRANES   OF   THE   CENTRAL 
NERVOUS  SYSTEM. 

The  membranes  of  the  central  nervous  system  (meninges)  are 
three  in  number:  the  outer,  or  dura  mater;  the  middle,  or  arach- 
noid ;  and  the  inner,  or  pia  mater. 

Around  the  brain  the  dura  mater  is  very  intimately  connected 
with  the  periosteum  and  presents  a  smooth  inner  surface.  It  con- 
sists of  an  inner  and  an  outer  layer,  the  two  being  separated  from 
each  other  only  in  certain  regions.  At  such  points  either  the  inner 
layer  is  pushed  inward  to  form  a  duplicature,  as  in  the  falx  cerebri 
and  falx  cerebelli,  tentorium,  and  diaphragma  sellae,  or  the  outer 
layer  is  pushed  outward  to  form  small,  blindly  ending  sacs.  The 
venous  and  lymphatic  sinuses  lie  between  the  two  layers.  The  outer 


394  THE    CENTRAL    NERVOUS    SYSTEM. 

layer  of  the  dura  is  continued  some  distance  along  the  cerebrospinal 
nerves. 

The  dura  mater  of  the  spinal  cord  does  not  form  the  periosteum 
for  the  bones  forming  the  vertebral  canal  ;  these  possess  their  own 
periosteum.  The  spinal  dura  mater  is  covered  on  its  outer  surface 
by  a  layer  of  endothelial  cells  and  is  separated  from  the  wall  of  the 
vertebral  canal  by  the  cpidural  space,  containing  a  venous  plexus 
imbedded  in  loose  areolar  connective  tissue  and  adipose  tissue. 

The  dura  consists  chiefly  of  connective-tissue  bundles  having  a 
longitudinal  direction  along  the  spinal  cord.  Within  the  cranium, 
however,  the  bundles  of  the  inner  and  outer  layers  cross  each  other  ; 
those  of  the  outer  having  a  lateral  direction  anteriorly  and  a  mesial 
posteriorly ;  those  of  the  inner,  a  mesial  direction  anteriorly  and  a 
lateral  posteriorly.  In  the  falx  cerebri,  tentorium,  etc.,  the  fibers  are 
arranged  radially,  extending  from  their  origin  toward  their  borders. 
The  shape  and  size  of  the  connective-tissue  cells  vary  greatly,  and 
their  processes  form  a  network  around  the  bundles  of  connective 
tissue.  Few  elastic  fibers  are  present,  and,  according  to  K.  Schultz, 
these  are  entirely  absent  in  the  new-born  ;  they  are  somewhat  more 
numerous  in  the  dura  of  the  spinal  cord.  The  dura  is  very  rich  in 
blood-capillaries,  and  the  presence  of  lymphatic  channels  in  com- 
munication with  the  subdural  space  may  be  demonstrated  by  means 
of  puncture-injections.  The  inner  surface  of  the  dura  mater  is  cov- 
ered by  a  layer  of  endothelial  cells. 

The  dura  mater  is  quite  richly  supplied  with  nerves,  especially 
in  certain  regions.  These  are  of  two  varieties  :  ( i)  Vasomotor  fibers, 
which  form  plexuses  in  the  adventitial  coat  of  the  arteries,  and 
would  seem  to  terminate  in  the  muscular  coat  of  the  arteries  ;  (2) 
medullated  nerve-fibers,  which  either  accompany  the  blood-vessels 
in  the  form  of  larger  or  smaller  bundles  or  have  a  course  inde- 
pendent of  the  vessels.  After  repeated  division  these  medullated 
nerve-fibers  lose  their  medullary  sheaths  and  terminate  between  the 
connective-tissue  bundles  in  fine  varicose  fibrils,  which  may  often 
be  traced  for  long  distances  (Huber,  99). 

The  arachnoid  is  separated  from  the  dura  by  a  space  which  is 
regarded  as  belonging  to  the  lymphatic  system — the  subdural  space. 
The  outer  boundary  of  the  arachnoid  consists,  as  does  the  inner  lin- 
ing of  the  dura,  of  a  layer  of  flattened  endothelial  cells.  The  arach- 
noid is  made  up  of  a  feltwork  of  loosely  arranged  connective-tissue 
trabeculae,  which  also  penetrate  into  the  lymph-space  between  it 
and  the  pia — the  siibarachnoid  space.  For  a  short  distance  from 
their  points  of  origin  the  cerebrospinal  nerves  are  accompanied  by 
arachnoid  tissue.  In  the  brain  the  arachnoid  covers  the  convolu- 
tions and  penetrates  with  its  processes  into  the  sulci.  These  pro- 
cesses are  especially  well  developed  in  the  so-called  cisterns  ;  in 
the  cisterna  cerebellomedullaris,  fossae  Sylvii,  etc.  In  the  spinal 
cord  the  subarachnoid  space  is  separated  by  the  ligamenta  den- 
ticulata  into  two  large  communicating  spaces — a  dorsal  and  a  ven- 


THE    MEMBRANES    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


395 


Gray 
matter. 


tral.      The  dorsal  space  is  further  divided  by  the  septum  posticum, 
best  developed  in  the  cervical  region. 

At  certain  points,  usually  along  the  superior  longitudinal  sinus, 
the  outer  surface  of  the  arachnoid  is  raised  into  villi,  which  are 
covered  by  the  inner  layer  of  the  dura,  and  form  with  the  latter  the 
Pacchionian  bodies  or  granulations.  These  villi  are  connected 
with  the  arachnoid  by  pedicles  so  delicate  that  they  often  seem  to 
be  suspended  free  in  the  venous  current  of  the  sinus. 

The  subarachnoid  space  contains  numerous  blood-vessels,  some 
of  which  are  free   and   others   attached   to  the  arachnoid.     Their 
adventitia  is  covered  by  endothelium  ;  hence  the  subarachnoid  space 
would  seem   to    assume 
here  the   character  of  a 
perivascular  space. 

The  trabeculae  and 
membranes  composing 
the  arachnoid  tissue  show 
a  great  similarity  to  those 
of  the  mesentery,  and  es- 
pecially to  those  of  the 
omentum.  The  whole 
constitutes  a  typical  are- 
olar  connective  tissue, 
interrupted  at  numerous 
points  and  covered  by  a 
continuous  layer  of  en- 
dothelial  cells.  Large 
numbers  of  spiral  fibers 
are  found  here  twining 
around  single  or  groups 
of  connective-tissue  fi- 
bers. 

The  pia  mater  cov- 
ers the  entire  surface  of 
the  brain  and  spinal  cord, 
dipping  down  into  every 
fissure  and  crevice.  In 
the  spinal  cord  it  con- 
sists of  an  outer  and  an  inner  lamella,  the  former  being  com- 
posed of  bundles  of  connective  tissue  containing  elastic  fibers. 
As  a  rule,  the  course  of  the  fibers  is  longitudinal.  Externally 
this  layer  is  covered  by  a  layer  of  endothelium.  The  blood- 
vessels lie  between  the  outer  and  inner  layers  of  the  pia.  The 
inner  layer  (pia  intima)  is  made  up  of  much  finer  elements,  and 
is  covered  on  both  sides  by  endothelium.  It  is  this  layer  which 
accompanies  the  blood-vessels  penetrating  into  the  spinal  cord, 
surrounding  their  adventitia  "and  forming  with  the  latter  the  limits 
of  their  perivascular  spaces.  These  are  in  communication  with  the 


y    White 
matter. 


Fig.  328. — Section  through  the  cerebral  cortex  of  a 
rabbit.     The  blood-vessels  are  injected ;  X  4°- 


396  THE    CENTRAL    NERVOUS    SYSTEM. 

interpial  spaces,  and,  by  means  of  the  adventitia  of  the  blood-vessels, 
with  the  subarachnoid  space.  Aside  from  those  just  described, 
numerous  fine,  nonvascular,  connective-tissue  septa  penetrate  from 
the  pia  mater  into  the  substance  of  the  spinal  cord.  Wherever  the 
pia  mater  penetrates  the  spinal  cord,  the  latter  is  hollowed  out, 
forming  the  so-called  pial funnels. 

The  pia  does  not  everywhere  lie  in  direct  contact  with  the  sur- 
face of  the  spinal  cord ;  for  between  the  cord  and  the  pia  there  is 
generally  found  a  neurogliar  covering,  formed  by  the  expanded 
ends  of  the  radial  processes  from  the  neurogliar  cells  (glia  covering 
or  subpia).  The  posterior  longitudinal  septum  of  the  spinal  cord 
consists  (in  the  thoracic  region)  exclusively  of  neurogliar  elements, 
but  in  the  cervical  and  lumbar  regions  the  pia  also  enters  into  its 
peripheral  formation. 

In  the  brain,  however,  the  conditions  are  somewhat  different. 
Here  the  external  layer  of  the  pia  disappears,  leaving  only  a  single 
layer  analogous  to  the  pia  intima  of  the  spinal  cord. 

The  pia  mater  enters  into  the  formation  of  the  choroid  plexus. 
This  structure  consists  of  numerous  freely  anastomosing  blood- 
vessels, which  form  villus-like  processes,  the  surfaces  of  which  are 
covered  by  squamous  or  cubic  epithelial  cells.  This  epithelium  is 
regarded  as  a  continuation  of  the  ventricular  epithelium,  and  is  cili- 
ated, at  least  in  embryonic  life  and  in  the  lower  classes  of  verte- 
brates. From  an  ernbryologic  point  of  view  the  whole  structure 
represents  the  brain-wall  reduced  to  a  single  layer  of  epithelium 
(internal  epithelial  investment)  pushed  forward  into  the  ventricle  by 
the  vessels  and  pia  mater. 

Since  the  dura  and  arachnoid  accompany  the  cerebrospinal 
nerves  for  some  distance,  it  is  obvious  that  the  lymph-vessels 
of  the  nasal  mucous  membrane  (see  these)  may  also  be  injected 
from  the  subarachnoid  space  (compare  also  Key  and  Retzius). 

The  pia  mater,  like  the  dura  mater,  receives  two  varieties  of 
nerve-fibers  :  (i)  Vasomotor  fibers,  which  form  plexuses  in  the  ad- 
ventitial  coat  of  the  arteries  and  terminate  in  the  muscular  layer  of 
the  arteries.  These  may  be  traced  to  the  small  precapillary 
branches  of  the  vessels.  (2)  Larger  and  smaller  bundles  of  rela- 
tively large,  medullated  nerve-fibers,  which  accompany  the  larger 
pial  vessels,  forming  loose  plexuses  in  or  on  the  adventitial  coat  of 
the  vessels.  After  repeated  divisions  these  medullated  nerves  lose 
their  medullary  sheaths  and  terminate,  in  the  adventitia  of  the  ves- 
sels, in  long,  varicose  fibrils  or  in  groups  of  such  fibrils  (Huber, 
99)- 


BLOOD-VESSELS    OF    THE    CENTRAL    NERVOUS    SYSTEM.  397 

J.  BLOOD-VESSELS  OF  THE  CENTRAL  NERVOUS 

SYSTEM. 

The  blood-vessels  of  the  central  nervous  system  present  certain 
peculiarities,  which  deserve  special  consideration. 

In  the  spinal  cord  the  arteries,  surrounded  by  pial  tissue  (con- 
nective-tissue septa),  extend  as  far  as  the  gray  matter,  but  give  off 
numerous  lateral  branches  during  their  course  through  the  white 
matter.  The  capillaries  form  a  much  closer  meshwork  in  the  gray 
matter  than  in  the  white. 

The  perivascular  spaces  throughout  the  central  nervous  system 
are  separated  from  the  substance  of  the  brain  and  spinal  cord  by 
an  endothelial  membrane,  the  internal  endothelial  layer  of  the  pia 
intima  (Key  and  Retzius),  and  are  easily  injected  from  the  pia. 

In  the  cerebral  cortex  the  capillaries  are  particularly  numerous, 
and  are  closely  meshed  wherever  groups  of  ganglion  cells  occur. 
In  the  medullary  substance  they  are  somewhat  less  closely  arranged, 
their  meshes  being  oblong. 

In  the  cerebellum  the  arrangement  is  analogous.  Of  all  the 
layers  composing  the  cerebellum  the  granular  is  the  most  vascu- 
lar ;  within  it  the  capillaries  are  also  densely  arranged,  and  form  a 
close  network. 

TECHNIC 

300.  The  organs  of  the  central  nervous  system  are  best  fixed  in  Mul- 
ler's  fluid  (vid.  T.  27),  washed  with  water,  cut  in  celloidin,  and  stained 
with    carmin.      Such  preparations  are  suitable  for  general    topographic 
work. 

301.  Special  structures — as,  for  instance,  the  medullary  sheaths  of  the 
nerve-fibers,  the  ganglion  cells,  the  relations  of  the  different  neurones  and 
dendrites  to  one  another,  etc. — require  different  treatment. 

302.  The  medullary  sheath  may  be  demonstrated  as  follows  (Wei- 
gert):     Pieces  of  tissue  (spinal  cord,  for  instance),  fixed  as  usual  in  Miil- 
ler's  or  Erlicki's  fluid  (vid.  T.  27  and  29),  are  transferred  without  wash- 
ing   to  alcohol,  imbedded  in  celloidin,   and  cut.      Before  staining  the 
sections  it  is  necessary  to  subject  them  to  the  mordant  action  of  a  neutral 
copper  acetate  solution  (a  saturated  solution  of  the  salt  diluted  with  an 
equal  volume  of  water).     The  sections  may  be  subjected  to  the  mordant 
action  of  this  solution,  but   the   following  procedure   is  more  conveni- 
ent :  The  specimens,  imbedded  in  celloidin  and  fastened  to  a  cork  or  a 
block  of  wood,  are  placed  for  one  or  two  days  in  the  copper  solution  just 
described.      At  the  expiration  of  this  time  the  pieces  of  tissue  will  have 
become  dark,  and  the  surrounding  celloidin  light  green.     They  are  then 
placed  in  80%  alcohol,  in  which  they  may  be  preserved  for  any  length 
of  time.     The  sections  are  then  stained  in  the  following  solution  :    i  gm. 
of  hematoxylin  is  dissolved  in   10  c.c.  absolute  alcohol,  and  90  c.c.  of 
distilled  water  are  then  added  (the  fluid  must  remain  exposed  to  the  air 
for  a  few  days)  ;   the  addition  of  an  alkali — as,  for  instance,  a  cold  satu- 
rated solution  of  lithium  bicarbonate  (i  c.c.  to  100  c.c.  of  hematoxylin 
solution) — brings  out  the  staining  power  of  the  solution  at  once.      In 


398  THE    CENTRAL    NERVOUS   SYSTEM. 

this  stain  the  sections  are  placed  (at  room -temperature)  for  a  day,  and 
then  in  a  thermostat  (40°  C.)  for  a  few  hours.  The  sections,  now  quite 
dark,  are  washed  in  distilled  water  and  then  placed  in  the  so-called  dif- 
ferentiating fluid.  The  latter  consists  of  borax  2  gm.,  ferrocyanid  of 
potassium  2.5  gm.,  and  distilled  water  100  gm.  In  this  fluid  the  color 
of  the  sections  is  differentiated  by  virtue  of  the  circumstance  that  the 
medullary  sheath  retains  the  dark  stain,  while  the  remaining  structures, 
such  as  the  ganglion  cells,  etc. ,  are  bleached  to  a  pale  yellow.  The  time 
required  for  this  differentiation  varies,  but  it  is  usually  complete  at  the  end 
of  a  few  minutes.  The  sections  are  then  washed  in  distilled  water,  dehy- 
drated in  alcohol,  cleared  in  carbol-xylol  (carbolic  acid  i  part,  xylol  3 
parts)  and  mounted  in  balsam. 

303.  Weigert's  new  method  is  more  complicated,  but  fruitful  of  cor- 
respondingly better  results.  The  preliminary  treatment  remains  the  same. 
After  the  tissues  have  been  imbedded  in  celloidin  and  this  hardened  in 
80%  alcohol,  they  are  transferred  to  a  mixture  composed  of  equal  parts 
of  a  cold  saturated  aqueous  solution  of  neutral  copper  acetate  and  10% 
aqueous  solution  of  sodium  and  potassium  tartrate,  and  the  whole  is  placed 
in  the  thermostat.  Larger  pieces — as,  for  instance,  the  pons  Varolii  of 
man — may  remain  in  the  solution  longer  than  twenty-four  hours,  after 
which  time,  however,  the  mixture  must  be  changed  ;  but  in  no  case  should 
the  specimens  be  permitted  to  remain  longer  than  forty -eight  hours  in 
this  solution.  The  temperature  in  the  thermostat  should  not  be  high, 
otherwise  the  specimens  will  become  brittle.  The  objects  are  now  placed 
in  a  simple  aqueous  solution  of  neutral  copper  acetate,  either  saturated 
or  half  diluted  with  water,  and  again  put  in  the  oven.  They  are  then 
rinsed  in  distilled  water  and  placed  in  80%  alcohol;  after  remaining 
in  this  for  one  hour,  they  are  in  a  condition  to  cut,  but  may  be  preserved 
still  longer  if  desired.  Cut  and  stain  in  the  customary  manner.  The 
staining  solution  is  prepared  as  follows :  (a)  lithium  carbonate  7  c.c.  and 
distilled  water  93  c.c.  (saturated  aqueous  solution)  ;  (^)  hematoxylin  i 
gm.,  absolute  alcohol  10  c.c.  ;  both  a  and  b  keep  for  some  time,  and  may 
be  kept  on  hand  as  stock  solutions.  Shortly  before  using,  9  parts  of  a 
and  i  part  of  b  are  mixed.  After  remaining  in  this  solution  for  from 
four  to  five  hours  at  room -temperature  the  sections  are  well  stained,  but 
do  not  overstain  even  if  allowed  to  remain  in  the  solution  for  twenty-four 
hours.  In  the  case  of  loose  celloidin  sections  the  use  of  the  differentiat- 
ing fluid  is  superfluous.  Hence  this  method  is  particularly  advantageous 
when  the  gray  and  the  white  matter  can  not  be  distinguished  macro- 
scopically.  Finally,  the  sections  are  washed  in  water,  placed  in  95% 
alcohol,  cleared  with  carbol-xylol  or  anilin-xylol  (in  the  latter  case 
carefully  washed  with  xylol),  and  mounted  in  xylol -balsam.  The  medul- 
lated  fibers  appear  dark  blue  to  black,  the  background  pale  or  light 
pink,  and  the  celloidin  occasionally  bluish.  In  order  to  remove  the  latter 
color,  it  is  only  necessary  to  wash  the  sections  in  0.5%  acetic  acid  in- 
stead of  ordinary  water ;  a  process,  however,  not  to  be  recommended 
in  the  case  of  very  delicate  preparations — as,  for  instance,  the  cerebral 
cortex.  In  applying  Weigert's  methods  a  certain  thickness  of  section 
(not  exceeding  25  /j.)  is  essential,  since  in  thicker  sections  the  medullary 
sheaths  are  not  sharply  differentiated  from  the  surrounding  tissue. 

For  thick  sections  the  modified  Weigert  method,  or  Pal's  method, 
is  employed.  After  the  specimens  have  been  treated  according  to  Wei- 


TECHNIC.  399 

gert's  method  up  to  the  point  of  staining  with  hematoxylin,  they  are  placed 
for  from  twenty  to  thirty  minutes  in  a  0.25%  solution  of  potassium  per- 
manganate. As  differentiating  fluid  a  solution  of  oxalic  acid  i  gm., 
potassium  sulphite  i  gm.,  and  water  200  c.c.  is  used,  care  being  taken, 
as  in  the  case  of  Weigert's  differentiating  fluid,  that  the  gray  matter  is 
thoroughly  bleached  (here  entirely  colorless)  and  the  white  matter  dark. 
By  this  method  the  medullary  sheaths  are  stained  blue,  while  the  rest  of 
the  structure  remains  colorless.  The  staining  is  very  precise,  but  not  so 
intense  as  by  Weigert's  method.  Hence  its  adaptability  for  thicker 
sections. 

Benda's  method  is  a  modification  of  the  Weigert-Pal  methods.  The 
tissues  are  hardened  in  Miiller's  or  Erlicki's  fluid,  imbedded  in  celloidin, 
and  cut.  The  sections  are  then  subjected  to  the  action  of  the  following 
mordant  for  from  twelve  to  twenty-four  hours  :  liquor  ferri  ter  sulphatis 
i  part,  distilled  water  2  parts.  They  are  then  thoroughly  rinsed  in  two 
tap-waters  and  one  distilled  water  and  then  stained  in  the  following  hem- 
atoxylin solution:  hematoxylin  i  gm.,  absolute  alcohol  10  c.c.,  distilled 
water  90  c.c.;  in  which  they  remain  for  twenty-four  hours.  They  are 
next  washed  in  tap -water  for  from  ten  to  fifteen  minutes  and  treated  with 
a  0.25%  aqueous  solution  of  permanganate  of  potassium  until  the  gray 
and  the  white  matter  are  differentiated,  after  which  they  are  rinsed  in 
distilled  water  and  bleached  in  the  following  solution  until  the  gray  mat- 
ter has  a  light  yellow  color  :  hydric  sulphite  5  to  10  parts,  distilled  water 
100  parts.  The  sections  are  then  washed  in  tap -water  for  from  one  to  two 
hours,  rinsed  in  distilled  water,  dehydrated,  cleared  in  carbol-xylol,  and 
mounted  in  balsam.  Medullary  sheaths  will  be  stained  a  bluish -black ; 
other  structures,  a  light  yellow.  Sections  stained  after  the  Weigert,  Pal, 
or  Benda  method  may  be  counterstained  in  Van  Gieson's  picric-acid- 
fuchsin  stain  ( i  c/0  aqueous  solution  of  acid  fuchsin,  1 5  parts  ;  saturated 
aqueous  solution  of  picric  acid,  50  parts;  distilled  water,  50  parts). 
The  fibrous  connective  tissue  in  the  sections  and  degenerated  areas  stains 
a  light  red. 

304.  Two  important  methods  have  lately  been  devised  for  the  dem- 
onstration of  ganglion  cells  with  their  processes  and  fibrils.     They  are 
Golgi's  chrome-silver  method  and  Ehrlich's  methylene-blue  method. 

305.  Golgi's  methods  will  perhaps  be  better  understood  if  we  first 
give  a  short  historic  sketch  of  their  development. 

In  the  year  1875  Golgi  applied  his  method  as  follows :  He  fixed  (olfactory  bulb)  in 
Miiller's  fluid,  and  increased  the  percentage  of  bichromate  on  changing  the  fluid  (up  to 
4  %}.  Fixation  lasted  five  or  six  weeks  in  summer  and  three  or  four  months  or  more 
in  winter.  He  then  took  out  pieces  of  the  tissue  every  four  or  five  days  and  treated  them 
experimentally  with  a  0.5%  to  \c/c  silver  nitrate  solution.  In  summer  this  process  took 
about  twenty-four  hours,  and  in  winter  forty-eight  hours,  although  a  longer  treatment 
was  not  found  to  be  detrimental.  This  method  must  be  regarded  as  very  uncertain,  since 
the  length  of  time  during  which  the  specimens  remain  in  Miiller's  fluid  must  be  very 
closely  calculated,  as  it  depends  largely  upon  the  temperature  of  the  medium.  As  soon 
as  the  silver  reaction  was  established,  the  pieces  were  preserved  either  in  the  silver  solu- 
tion itself  or  in  alcohol.  The  sections  were  finally  washed  in  absolute  alcohol,  cleared 
with  creosote,  and  mounted  in  Canada  balsam.  The  impregnation  disappeared  in  a 
short  time.  In  the  year  1885  Golgi  made  a  further  announcement  regarding  his  method, 
recommending  for  fixation  the  pure  bichromate  of  potassium,  as  well  as  Miiller's  fluid. 
Pieces  of  the  brain  and  spinal  cord  (from  I  to  1.5  c.c.  in  size)  from  a  freshly  killed  ani- 
mal were  used,  and  the  reaction  sometimes  took  place  in  from  twenty-four  to  forty-eight 
hours  after  death.  For  fixing,  potassium  bichromate  solution  in  gradually  ascending 
strengths  (l%  to  5$,)  was  employed,  large  amounts  of  the  fluid  being  used  and  placed 


4QO  THE    CENTRAL    NERVOUS    SYSTEM. 

in  well-sealed  receptacles.  The  fluid  was  repeatedly  changed,  and  camphor  or  salicylic 
acid  was  added  in  order  to  prevent  the  growth  of  fungi.  Since  it  is  difficult  to  determine 
exactly  when  fixation  in  potassium  bichromate  reaches  the  precise  point  favorable  to  sub- 
sequent treatment  with  nitrate  of  silver,  because  the  process  depends  entirely  upon  the 
temperature  and  quantity  of  the  fluid,  it  becomes  necessary,  after  about  six  weeks'  treat- 
ment with  the  bichromate,  to  experiment  every  eight  days  or  so  to  see  whether  the 
silver  nitrate  gives  good  results.  The  strength  of  the  latter  should  be  about  0.66%  and 
the  quantity  about  200  c.c.  to  a  I  c.c.  object.  At  first  a  plentiful  precipitate  is  thrown 
down,  in  which  case  the  solution  should  be  changed,  and  this  probably  repeated  once  more 
after  a  few  hours.  After  twenty-four  hours,  at  the  most  forty-eight  hours,  this  process  is 
usually  completed,  and  the  tissues  may  be  sectioned.  The  sections  must  then  be  care- 
fully dehydrated  with  absolute  alcohol,  cleared  in  creosote  and  mounted  without  a  cover- 
glass  in  Canada  balsam  (the  section  is  mounted  on  a  cover-glass  with  Canada  balsam,  and 
the  cover-slip  then  fastened  over  the  opening  of  a  perforated  slide  with  the  specimen 
downward). 

306.  In    order  to  obtain  a    uniform  penetration  of   the  objects  by  the  potassium 
bichromate,  the  latter  may  be  first  injected    into  the  vessels.       Golgi  uses   potassium 
bichromate-gelatin  (2.5^  of  the  salt,  based  on  the  amount  of  the  softened  gelatin  ;  com- 
pare Golgi,  93).     After  the  injection  and  cooling  of  the  specimen  the  latter  is  cut  in 
small  pieces  and  treated  in  the  manner  previously  described.      Instead  of  Miiller's  fluid, 
that  of  Erlicki  may  be  used,  the  time  of  treatment  being  then  shorter  (from  five  to  eight 
days). 

The  objects  may  also  be  treated  with  a  potassium  bichromate-osmic  acid  solution 
(2.5%  solution  of  potassium  bichromate,  8  vols. ;  \<f0  osmic  acid,  2  vols.),  the  sections 
thus  treated  being  ready  for  immersion  in  silver  nitrate  after  two  or  three  days.  It  is  ad- 
visable to  treat  the  objects  with  the  potassium  bichromate  solution  first,  and  then  with  the 
potassium  bichromate-osmic  mixture.  By  this  method  the  specimens  remain  under  the 
control  of  the  investigator ;  they  may  be  examined  either  at  once,  or  after  an  interval 
varying  between  three  or  four  and  twenty-five  to  thirty  days  after  immersion.  If  then  one 
or  several  pieces  of  tissue  are  taken,  at  intervals  of  two,  three,  or  four  days,  from  the  potas- 
sium bichromate  solution  and  placed  in  the  potassium  bichromate-osmic  acid  mixture, 
and  then  in  the  silver  nitrate  solution,  various  combinations  of  the  fluids  result,  and  the 
investigator  is  usually  rewarded  with  at  least  some  sections  giving  most  excellent 
results. 

307.  Another  one  of  Golgi' s  methods  consists  in  successive  treatment  with  potassium 
bichromate  and  bichlorid  of  mercury.     After  remaining  in  the  potassium  bichromate  for 
from  three  to  four  weeks  (a  longer  period  is  allowable),  the  objects  are  placed  in  a  0.25% 
to  I  %  solution  of  corrosive  sublimate.     In  the  latter  the  specimens  blacken  much  more 
slowly  than  in  the  silver  nitrate  solution — eight  to  ten  days  for  smaller  pieces  ;  for  larger 
ones,  two  months,  and  in  some  cases  even  longer.      Before  mounting  the  preparations  in 
glycerin  or  Canada  balsam  they  must  be  carefully  washed  ;  otherwise  pin-shaped  crystals 
form  within  the  sections  and  distort  the  whole  view.     The  metallic  white  of  the  prepara- 
tion may  be  changed  to  black  by  placing  the  celloidin  section  in  a  photographer's  toning 
solution  consisting  of :  (a)  sodium  hyposulphite  175  gm.,  alum  20  gm.,  ammonium  sulpho- 
cyanid  10  gm.,  sodium  chlorid  40  gm.,  and  water  looo  gm.  (the  mixture  must  stand  for 
eight  days  and  then  be  filtered)  ;  (t>]  a  I  %  gold  chlorid  solution.     The  specimen  is- 
placed  for  a  few  minutes  in  a  solution  composed  of  60  c.c.  of  a  and  7  c.c.  of  b,  washed 
again  in  distilled  water,  dehydrated  with  alcohol,  and  mounted  in  Canada  balsam.     After 
toning  and  washing,  the  sections  may  still  be  stained. 

Golgi' s  methods  are  extremely  inconstant  in  their  results.  When  successful,  how- 
ever, only  a  few  elements  are  blackened  each  time,  an  advantage  not  to  be  underesti- 
mated ;  for  if  all  nerves  should  stain  equally  well,  discrimination  between  the  various 
elements  in  the  preparation  would  be  very  difficult.  Neither  are  the  same  structures 
always  impregnated  ;  sometimes  it  is  the  ganglion  cells  and  fibers,  at  other  times  the  neu- 
rogliar  cells,  and  occasionally  only  the  vessels. 

After  the  foregoing  explanation  of  Golgi 's  methods  as  applied  by 
himself,  we  shall  append  a  description  of  these  methods  as  modified  and 
employed  at  the  present  time  (Ramon  y  Cajal,  Kolliker,  von  Lenhossek 
and  others). 

Golgi 's  methods  are  classified  as  the  slow,  the  mixed,  and  the  rapid. 

The  slow  method  requires  a  preliminary  treatment.  Pieces  of  tis- 
sue from  i  to  2  cm.  in  diameter  are  placed  for  from  three  to  five  weeks 


TECHNIC.  4OI 

in  a  2  r/o  potassium  bichromate  solution  ;  they  are  then  transferred  for  from 
twenty-four  to  forty-eight  hours  to  a  0.75%  silver  nitrate  solution,  or  for 
a  much  longer  time  to  a  0.5%  solution  of  corrosive  sublimate. 

In  the  mixed  method  the  specimens  are  allowed  to  remain  for  four 
or  five  days  in  a  2  %  aqueous  potassium  bichromate  solution  ;  then  for 
from  twenty-four  to  thirty  hours  in  a  mixture  consisting  of  i%  osmic 
acid  i  vol.,  and  2%  potassium  bichromate  solution  4  vols.  They  are 
then  treated  with  a  0.75%  silver  nitrate  solution  for  one  or  two  days. 

When  the  rapid  method  is  employed,  the  specimens  are  immedi- 
ately placed  in  a  mixture  consisting  of  i  vol.  of  i%  osmic  acid  and  4 
vols.  of  a  3.5%  potassium  bichromate  solution,  and,  finally,  for  one  or 
two  days  in  a  0.75%  silver  nitrate  solution,  to  every  200  c.c.  of  which 
one  drop  of  formic  acid  has  been  added. 

When  employing  these  methods,  and  more  particularly  the  one  last 
described  (which  seems  to  be  the  most  efficient),  the  following* conditions 
must  be  carefully  observed  :  If  possible,  the  material  should  be  absolutely 
fresh,  the  specimens  must  not  exceed  3  or  4  mm.  in  thickness,  and  for 
every  piece  of  tissue  treated  about  10  c.c.  of  the  osmium -potassium 
bichromate  mixture  should  be  employed,  the  specimens  remaining  in  the 
latter  (in  the  dark)  at  a  temperature  of  25°  C.  for  a  length  of  time  vary- 
ing according  to  the  result  desired  (two  or  three  days  for  the  neurogliar 
cells,  from  three  to  five  days  for  the  ganglion  cells,  and  from  five  to  seven 
days  for  the  nerve-fibers  of  the  spinal  cord).  The  objects  are  now  dried 
with  blotting-paper  or  washed  quickly  in  distilled  water  and  then  placed 
for  two  or  three  days  in  a  0.75%  silver  nitrate  solution  at  room-tempera- 
ture. In  this  they  may  remain  for  four  or  five  days  without  damage,  but 
not  longer,  as  otherwise  the  precipitate  becomes  markedly  granular  (irid. 
v.  Lenhossek,  92). 

308.  If  Golgi's  method  be  unsuccessful  (this  applies  to  all  its  modifica- 
tions), the  preparations  may  be  transferred  from  the  silver  nitrate  solu- 
tion   back    into  a  potassium  bichromate-osmic  acid  mixture  containing 
less  osmic  acid,  in  which  they  remain  several  days,  and  are  then  again 
placed  in  the  silver  nitrate  solution  for  from  twenty-four  to  forty -eight 
hours.     This  procedure  may  even  be  repeated. 

309.  Cox  obtains  a  precipitate  in  both  cells  and  fibers  by  treating 
small  pieces  of  the  central  nervous  organs  with  a  mixture  composed  of 
potassium  bichromate  20  parts,  5%  corrosive  sublimate  20  parts,  distilled 
water  30  to  40  parts,  and  5%   potassium  chromate  of  strong  alkaline 
reaction  16  parts.     The  specimens  remain  in  this  mixture  from  one  to 
three  months,  according  to  the  temperature,  and  are  then  further  treated 
according  to  Golgi's  method. 

As  the  chrome-silver  preparations  are  not  permanent,  and  can  not, 
therefore,  be  subsequently  stained,  Kallius  has  suggested  that  the  chrome- 
silver  precipitate  be  reduced  to  metallic  silver  by  treatment  with  the 
"  quintuple  hydroquinon  developer"  (hydroquinon  5  gm.,  sodium 
sulphite  40  gm.,  potassium  carbonate  75  gm.,  and  distilled  water  250 
gm.).  For  this  purpose  20  c.c.  of  the  solution  are  diluted  with  230  c.c. 
of  distilled  water  ;  this  mixture  may  be  preserved  in  the  dark  for  some 
time  if  desired.  Before  using  this  latter  solution,  it  should  be  mixed  with 
y?,,  or  at  the  most  ^,  of  its  volume  of  absolute  alcohol.  The  sections  are 
placed  in  a  watch-crystal  containing  some  of  the  latter  mixture  until  they 
turn  black  (a  few  minutes).  As  soon  as  the  silver  salt  is  completely 
26 


402 


THE    CENTRAL    NERVOUS    SYSTEM. 


reduced,  the  sections  are  placed  for  from  ten  to  fifteen  minutes  in  70% 
alcohol,  then  for  five  minutes  in  a  20%  solution  of  sodium  hyposulphite 
and,  finally,  washed  for  some  time  in  distilled  water,  after  which  they 
may  be  stained,  and  even  treated  with  acid  alcohol  and  potassium 
hydrate. 

The  following  simple  method  for  permanently  mounting  Golgi  prepar- 
ations under  a  cover-glass  has  been  recommended  by  Huber. 

After  impregnation  with  chrome-silver  the  tissues  are  hastily  dehy- 
drated, imbedded  in  celloidin,  and  cut  in  sections  varying  from  25  //  to 
100  fjL  in  thickness.  The  sections  are  then  dehydrated  and  placed  for 
from  ten  to  fifteen  minutes  in  creosote,  from  which  they  are  carried 
into  xylol,  where  they  remain  another  ten  minutes.  The  sections  are 
then  removed  to  the  slide.  The  xylol  is  then  removed  by  pressing  sev- 
eral layers  of  filter-paper  over  the  section.  On  removing  the  filter-paper 
the  sections  are  quickly  covered  by  a  large  drop  of  xylol  balsam  and  the 
slide  is  carefully  heated  over  a  flame  for  from  three  to  five  minutes.  Be- 
fore the  balsam  cools  the  preparation  is  covered  with  a  large  cover-glass, 
warmed  by  passing  several  times  through  the  flame. 

310.  Kopsch  (96)  places  specimens  in  a  solution  composed  of  10  c.c. 
of  formalin  (40%  formaldehyd)  and  40  c.c.  of  a  3.5%  solution  of  potas- 
sium bichromate.      For  objects  2  c.c.  in  size  50  c.c.  of  the  fluid  are  em- 
ployed ;  but  if  the  specimens  be  large,  the  mixture  must  be  changed  in 
twelve  hours.     At  the  end  of  twenty -four  hours  this  fluid  is  replaced  by  a 
fresh  3.5%  potassium  bichromate  solution,  and  the  specimens  are  then 
transferred  to  a  0.75%  solution  of  silver  nitrate  (after  two  days,  if  the 
tissue  be  the  liver  or  stomach ;  and  after  from  three  to  six  days,  if  retina 
or  central  nervous  system).     After  this  treatment  the  objects  are   car- 
ried over  into  40%  alcohol  and,  finally,  into  absolute  alcohol,  imbedded 
as  rapidly  as  possible,  and  cut.     The  sections  are  mounted  in  balsam 
without  a  cover-glass. 

311.  Ehrlich's  methylene-blue  method  consists   in  an  infra  vitam 
staining  of  ganglion  cells,  nerve-fibers,  and  nerve-endings.     The  method 
is  much  more  applicable  to  the  staining  of  peripheral  ganglia  (spinal  and 
sympathetic  ganglia),  peripheral  nerves,  and  nerve-endings  than  to  stain- 
ing the  elements  of  the  central  nervous  system,  although  the  latter  may 
also  be  stained  by  means  of  this  method. 

Two  methods  for  bringing  the  stain  in  contact  with  the  nerve-tissues 
are  now  in  use  :  (i)  injecting  the  methylene-blue  solution  into  the  living 
tissues  through  the  blood-vessels  ;  ( 2 )  adding  a  few  drops  of  the  stain  to 
small  pieces  of  perfectly  fresh  tissues  removed  from  the  body.  The  solu- 
tion used  for  injecting  the  tissues  is  prepared  as  follows  :  i  gm.  of  methyl- 
ene-blue1 is  mixed  in  a  small  flask  with  100  c.c.  of  normal  salt  solution 
and  heated  over  a  flame  until  the  solution  becomes  hot.  It  is  then  allowed 
to  cool ;  when  filtered,  it  is  ready  for  use.  A  cannula  is  tied  into  the 
main  artery  of  the  part  in  which  it  is  desired  to  stain  the  nerve  elements, 
and  sufficient  of  the  foregoing  methylene-blue  solution  injected  to  give 
the  part  a  decidedly  blue  color.  After  the  injection  the  part  to  be 
studied  remains  undisturbed  for  about  one-half  hour,  after  which  time 
small,  or  at  least  thin,  pieces  of  the  tissue  to  be  studied  are  removed  to  a 
slide  moistened  in  normal  salt  solution,  and  exposed  to  the  air.  The 
tissues  remain  on  the  slide  until  the  nerve-cells,  nerve-fibers,  or  nerve- 

1  Methylenblau,  rectificiert  nach  Ehrlich,  Grubler,  Leipzig. 


TECHNIC.  403 

endings  seem  satisfactorily  stained.  After  placing  the  tissues  on  the  slide, 
they  are  examined  under  the  microscope  (without  covering  with  a  cover- 
glass)  every  two  or  three  minutes,  until  such  examination  shows  blue 
color  in  the  neuraxes  of  the  nerve-fibers  and  their  terminations,  or  in  the 
nerve-cells,  if  there  be  any  in  the  tissues  examined.  Care  should  be 
taken  not  to  miss  the  time  when  the  staining  has  reached  its  full  develop- 
ment, as  the  blue  color  usually  fades  again  and  only  inferior  preparations 
are  obtained. 

Tissues  thus  stained  may  be  fixed  by  one  of  two  methods  (or  modifi- 
cations of  these  methods),  the  selection  of  the  method  depending  some- 
what on  the  results  desired.  If  it  is  desired  to  gain  preparations  giving 
the  general  course  of  nerves,  the  formation  of  nerve-plexuses,  the  relations 
of  afferent  and  efferent  nerves  to  the  nerve-cells  in  ganglia,  or  the  gen- 
eral arrangement  of  the  terminal  branches  of  nerve-fibers  in  nerve  end- 
organs,  the  tissues  are  placed  in  a  saturated  aqueous  solution  of  ammo- 
nium picrate  (Dogiel)  in  which  the  blue  color  of  the  tissues  is  in  a  short 
time  changed  to  a  purplish  color.  In  this  solution  the  tissues  remain  for 
from  twelve  to  twenty-four  hours,  and  are  then  transferred  to  a  mixture 
consisting  of  equal  parts  of  a  saturated  aqueous  solution  of  ammonium 
picrate  and  glycerin,  in  which  they  remain  another  twenty-four  hours ; 
they  may,  however,  without  detriment  remain  in  the  mixture  several 
days.  The  tissues  are  then  mounted  in  this  ammonium  picrate-glycerin 
mixture. 

If,  on  the  other  hand,  it  is  desired  to  section  tissues  stained  intra 
ritain  in  methylene-blue,  the  following  method,  slightly  modified  from 
that  given  by  Bethe,  is  suggested.  The  following  fixative  is  prepared  : 
Ammonium  molybdate,  i  gm.;  distilled  water,  10  c.c.;  hydrochloric 
acid,  i  drop.  The  solution  is  prepared  by  grinding  the  ammonium 
molybdate  to  a  fine  powder,  removing  it  to  a  flask,  and  adding  the 
required  quantity  of  water.  The  flask  is  now  heated  until  the  ammonium 
molybdate  is  entirely  dissolved,  when  the  hydrochloric  acid  is  added. 
Before  using  this  fixative  it  is  necessary  to  cool  it  to  2°-5°  C.  It  is,  there- 
fore, well  to  prepare  it  before  the  injection  is  made,  and  surround  it  with 
an  ice  mixture.  In  this  fixative  the  tissues  remain  for  from  twelve  to 
twenty-four  hours.  After  the  first  six  to  eight  hours  it  is  not  necessary  to 
keep  the  fixative  below  ordinary  room-temperature.  After  fixation  the 
tissues  are  washed  for  an  hour  in  distilled  water.  They  are  then  hard- 
ened and  dehydrated  in  absolute  alcohol.  It  is  advisable  to  hasten  this 
step  as  much  as  possible,  though  not  at  the  risk  of  imperfect  dehydration. 
The  tissues  are  then  transferred  to  xylol  and  imbedded  in  paraffin,  sec- 
tioned, fixed  to  the  slide  or  cover-glass  with  albumin  fixative,  and  may 
be  double  stained  in  alum-carmin  or  alum-cochineal.  After  staining  in 
either  of  these  stains,  the  sections  are  thoroughly  dehydrated  and  cleared 
in  oil  ofbergamot.  The  oil  is  washed  off  with  xylol  and  the  sections  are 
mounted  in  Canada  balsam. 

312.  In  staining  nerve-fibers  with  methylene-blue  by  local  application 
of  the  stain  to  the  tissues,  the  tissues  to  be  studied  are  removed  from  an 
animal  which  has  just  been  killed,  divided  in  small  pieces,  and  placed  on 
a  slide  moistened  with  normal  salt  solution.  A  few  drops  of  a  -fac/(  to 
TV%  solution  of  methylene-blue  in  normal  salt  solution  are  added  from 
time  to  time — sufficient  to  keep  the  tissues  moistened  by  the  solution,  but 
not  enough  to  cover  them.  The  preparations  are  examined  from  time  to 


404  THE    CENTRAL    NERVOUS    SYSTEM. 

time,  under  the  microscope,  to  see  whether  the  nerve  elements  are  stained. 
The  length  of  time  required  for  staining  by  this  method  varies.  Some- 
times the  nerve  elements  are  stained  in  half  an  hour ;  again,  it  may  re- 
quire two  and  one-half  hours  ;  on  an  average,  about  one  hour.  As  soon 
as  the  tissues  seem  well  stained  they  are  fixed  as  previously  directed. 
Dogiel  has  found  that  sympathetic  ganglia  and  sensory  nerve -fibers  of  the 
heart  removed  from  the  human  body  several  hours  after  death  may  be 
stained  by  means  of  the  foregoing  method. 

In  order  to  obviate  the  necessity  for  the  low  temperature  of  the  pre- 
vious method,  Bethe  (96)  has  recommended  the  following  procedure  : 
According  to  the  method  of  Smirnow  and  Dogiel,  he  first  employs  as  a 
preliminary  fixing  agent  a  concentrated  aqueous  solution  of  ammonium 
picrate.  In  this  he  places  the  tissue,  previously  treated  with  methylene- 
blue,  for  from  ten  to  fifteen  minutes.  Without  further  washing  the  larger 
objects  are  immersed  in  a  mixture  composed  of  ammonium  molybdate 
(or  sodium  phosphomolybdate)  i  gm.,  distilled  water  20  c.c.,  and  pure 
hydrochloric  acid  i  drop.  The  following  mixtures  may  also  be  employed 
for  the  same  purpose :  ammonium  molybdate  (or  sodium  phosphomo- 
lybdate) i  gm.,  distilled  water  10  c.c.,  2%  solution  of  chromic  acid 
10  c.c.,  and  hydrochloric  acid  i  drop  ;  or,  for  very  thin  gross  specimens 
or  sections,  ammonium  molybdate  (or  sodium  phosphomolybdate)  i  gm., 
distilled  water,  10  c.c.,  0.5%  osmic  acid  10  c.c.,  and  hydrochloric  acid 
i  drop.  Small  objects  are  permitted  to  remain  no  longer  than  from  three 
quarters  of  an  hour  to  one  hour  in  either  of  the  first  two  mixtures,  and 
not  more  than  from  four  to  twelve  hours  in  the  third.  After  fixing,  the 
specimens  are  washed  with  water,  carried  over  into  alcohol,  then  into  xylol, 
and  finally  imbedded  in  paraffin.  Subsequent  staining  with  alum-carmin, 
alum-cochineal,  or  one  of  the  neutral  anilin  dyes  gives  good  results. 

313.  A  very  promising  method  recommended  by  Meyer  (95)  consists 
in  injecting  subcutaneously  about  20  c.c.  of  normal  salt  solution  contain- 
ing from  i%  to  4%  of  methylene-blue  into  a  young  rabbit,  and  repeating 
the  operation  in  one  to  two  hours.     Within  the  next  two  hours  the  animal 
usually  dies  and  the  central  nervous  organs  are  then  removed  and  small 
pieces  fixed  according  to  Bethe's  method. 

314.  Apathy  (97)  demonstrates  the  fibrillar  elements  of  the  nervous 
system  in  invertebrates  and  vertebrates  by  means  of  his  gold  method. 
Fresh  tissue  may  be  used,  or  tissue  already  fixed.      In  the  first  case  thin 
membranes  are  placed  for  at  least  two  hours  in  a  i  %  solution  of  yellow 
chlorid  of  gold  in  the  dark,  then  carried  over  without  washing  into  a  i% 
solution  of  formic  acid  (sp.   gr.    1.223),  and  finally  exposed  for  from 
six  to  eight  hours  to  the  light  (the  formic  acid  may  have  to  be  changed). 
These  specimens  are  best  mounted  directly  in  syrup  of  acacia  or  in  con- 
centrated glycerin.     In  his  second  method  Apathy  fixes  vertebrate  tissues 
for  twenty-four  hours  in  sublimate-osmic  acid  (i  vol.  saturated  solution 
of  corrosive  sublimate  in  0.5%  sodium  chlorid  solution  combined  with  i 
vol.  \°/o  osmic  acid  solution),  washes  repeatedly  in  water,  and  places  for 
twelve  hours  in  an  aqueous  iodo-iodid  of  potassium  solution  (potassium 
iodid  i  %  and  iodin  0.5%).    The  further  treatment  is  the  same  as  after  or- 
dinary corrosive  sublimate  fixation.      Finally,  the  specimens  are  imbedded 
in  paraffin  with  the  aid  of  chloroform,  cut,  and  mounted  by  the  water 
method.       The  whole  process,  up  to  the  point  of  imbedding  in  paraffin, 
is  carried  out  in  the  dark.     The  sections  are  then  passed  through  chloro- 


TECHNIC.  405 

form  and  alcohol  into  water,  where  they  are  allowed  to  remain  for  at  least 
six  hours  ;  or  they  may  be  washed  in  water,  placed  for  one  minute  in  i  % 
formic  acid,  again  washed  in  water,  immersed  for  twenty-four  hours  in  a 
i  c/0  solution  of  gold  chlorid,  rinsed  in  water,  and  finally  placed  in  a  i  °/0 
formic  acid  solution  and  exposed  to  the  light.  For  the  latter  purpose 
glass  tubes  are  employed  in  which  the  slides  are  placed  obliquely,  with  the 
sections  downward.  A  uniform  illumination  of  the  section  with  "  as 
intense  a  light  and  low  a  temperature  "  as  possible  are  conditions  indis- 
pensable to  the  attainment  of  successful  results.  The  sections  are  then 
again  washed  in  water  and  mounted  in  glycerin  or  syrup  of  acacia,  or  in 
Canada  balsam  after  being  dehydrated.  Thin  membranes  are  stretched 
upon  small  frames  of  linden  wood  especially  prepared  for  this  purpose. 
Their  further  treatment  is  then  the  same  as  that  of  sections  fixed  to  the  slide. 
If  successful,  the  nerve-fibrils  appear  dark  violet  to  black.  The  large 
ganglia  in  the  spinal  cord  of  lophius,  the  calf,  etc.,  are  especially  recom- 
mended as  appropriate  vertebrate  material. 

Bethe  (1900)  has  recommended  the  following  method  for  staining 
neurofibrils  and  Golgi-nets  in  the  central  nervous  system  of  vertebrates  : 

The  perfectly  fresh  tissue  is  cut  in  thin  lamellae,  varying  in  thickness 
from  4  to  10  mm.  These  are  placed  on  pieces  of  filter-paper  and 
then  in  3  to  7.5%  nitric  acid,  in  which  they  remain  twenty-four  hours. 
From  the  hardening  fluid  the  pieces  of  tissue  are  transferred  into  96% 
alcohol,  where  they  remain  for  from  twelve  to  twenty-four  hours.  They 
are  then  placed  in  a  solution  of  ammonium -alcohol, — ammonium  (sp.  gr. 
0.95  to  0.96),  i  part;  distilled  water,  3  parts;  96%  alcohol,  8  parts, — 
in  which  they  remain  for  from  twelve  to  twenty-four  hours.  The  temper- 
ature of  this  solution  should  not  exceed  20°  C.  The  tissues  are  then 
placed  for  from  six  to  twelve  hours  in  96%  alcohol,  and  next  in  a  hydro- 
chloric acid-alcohol  solution, — concentrated  hydrochloric  acid  (sp.  gr. 
1. 1 8 — 37%),  i  part;  distilled  water,  3  parts;  and  96%  alcohol,  8  to  12 
parts, — in  which  they  remain  for  several  hours.  The  temperature  of  this 
solution  should  not  exceed  20°  C.  The  tissues  are  then  again  placed  in 
96%  alcohol  for  from  ten  to  twenty-four  hours,  and  next  in  distilled  water 
for  from  two  to  six  hours.  The  tissues  are  now  placed  for  twenty-four 
hours  in  a  4%  aqueous  solution  of  ammonium  molybdate.  (This  solution 
should  be  kept  at  a  temperature  varying  from  10°  to  15°  C.,  if  it  is  de- 
sired to  stain  the  neurofibrils ;  or  at  a  temperature  varying  from  10°  to 
30°  C.,  if  it  is  desired  to  bring  out  the  Golgi-nets.)  After  the  ammo- 
nium molybdate  treatment,  the  tissues  are  rinsed  in  distilled  water,  placed 
in  96%  alcohol  for  from  ten  to  twenty-four  hours,  then  in  absolute  alco- 
hol for  a  like  period,  cleared  in  xylol  or  toluol,  and  imbedded  in  par- 
affin. Sections  having  a  thickness  of  10  //  are  now  cut  and  fixed  to  slides 
with  Mayer's  albumin-glycerin.  Since  the  various  solutions  used  in  the 
fixation  and  further  treatment  of  the  tissues  do  not  act  with  the  same  in- 
tensity on  all  parts  of  the  piece  of  tissue  to  be  studied,  and  since  the  differ- 
entiation and  staining  depend  on  a  relative  proportion  (not  yet  fully  de- 
termined) of  the  mordant  (ammonium  molybdate)  and  the  stain  in  a 
given  section,  it  is  advised  by  Bethe  to  cut  large  numbers  of  sections  and 
fix  to  each  slide  about  three  sections  from  different  parts  of  the  series. 
After  fixation  of  the  sections  to  the  slide  the  paraffin  is  removed  with 
xylol ;  and  they  are  then  carried  through  absolute  alcohol  into  distilled 
water,  in  which,  however,  the  sections  remain  only  long  enough  to  re- 


406  THE    CENTRAL    NERVOUS    SYSTEM. 

move  the  alcohol.  The  slides  (with  the  sections  fixed  to  them)  are  then 
taken  from  the  water  and  rinsed  with  distilled  water  from  a  water-bottle. 
The  slide  is  then  wiped  dry  on  its  under  surface  and  edges  with  a  clean 
cloth,  and  about  i  c.c.  to  1.5  c.c.  of  distilled  water  placed  on  the  slide 
over  the  sections.  The  slides  are  now  placed  in  a  warm  oven  with  a  tem- 
perature of  55°  C.  to  60°  C.  for  a  period  of  time  varying  from  two  to 
ten  minutes.  No  definite  time  can  here  be  given  ;  sections  from  each 
block  of  tissue  need  to  be  tested  until  the  right  stay  in  the  warm  oven  is 
ascertained.  The  slides  are  then  taken  from  the  warm  oven  and  rinsed 
two  or  three  times  in  distilled  water  and  again  dried  as  previously 
directed.  They  are  then  covered  with  the  following  staining  solution 
and  again  placed  in  the  warm  oven  for  about  ten  minutes  :  toluidin-blue, 
i  part ;  distilled  water,  3000  parts.  The  stain  is  washed  off  with  dis- 
tilled water  and  the  sections  are  placed  in  96%  alcohol  until  no  more 
stain  is  given  off — usually  for  from  three-fourths  to  two  minutes.  They 
are  then  dehydrated  in  absolute  alcohol,  passed  through  xylol  twice,  and 
mounted  in  xylol  balsam.  For  a  fuller  discussion  of  this  method  the 
reader  is  referred  to  Bethe's  account  in  ' '  Zeitsch.  f.  Wissensch.  Mikrosk. , ' ' 
vol.  xvn,  1900. 

315.  For  staining  neuroglia  Weigert  (95)  has  recommended  a 
method,  from  which  we  give  the  following  :  A  solution  is  made  consisting 
of  5%  neutral  acetate  of  copper,  5%  ordinary  acetic  acid,  and  2.5% 
chrome-alum  in  water.  The  chrome-alum  and  water  are  first  boiled 
together,  the  acetic  acid  then  added,  and  finally  the  finely  pulverized 
neutral  copper  acetate,  after  which  the  mixture  is  thoroughly  stirred  and 
allowed  to  cool.  To  this  solution  10%  formalin  may  be  added.  Objects 
not  over  0.5  cm.  in  diameter  are  placed  in  this  fluid  for  eight  days,  the 
mixture  being  changed  at  the  end  of  a  few  days.  By  this  means  the 
pieces  of  tissue  are  at  the  same  time  fixed  and  prepared  for  subsequent 
staining  by  the  action  of  the  mordant.  If  separation  of  the  two  processes 
be  desired,  the  specimens  are  fixed  for  about  four  days  in  a  10%  formalin 
solution  (which  is  changed  in  a  few  days),  and  then  placed  in  the 
chrome-alum  mixture  without  the  addition  of  formalin.  Specimens  thus 
fixed  may  be  preserved  for  years  without  disadvantage,  and  may  then  be 
subjected  to  further  treatment  by  other  methods,  Golgi's  for  instance. 
Washing  with  water,  dehydration  in  alcohol,  and  imbedding  in  celloidin 
are  the  next  steps.  The  sections  are  then  placed  for  about  ten  minutes 
in  a  0.33%  solution  of  potassium  permanganate,  washed  by  pouring  water 
over  them,  and  placed  in  the  reducing  fluid  (5%  chromogen  and  5% 
formic  acid  of  a  specific  gravity  of  1.20;  then  filter  carefully,  and 
add  10  c.c.  of  a  10%  solution  of  sodium  sulphite  to  90  c.c.  of  the  fluid). 
The  sections,  rendered  brown  by  the  potassium  permanganate,  readily 
decolorize  in  a  few  minutes,  but  it  is  better  to  leave  them  for  from  two  to 
four  hours  in  the  solution.  If  it  be  desirable  to  decolorize  entirely  the 
connective  tissue,  no  further  steps  need  be  taken  preliminary  to  staining  ; 
if  not,  the  reducing  fluid  is  poured  off  and  the  sections  are  rinsed  twice 
in  water  and  then  placed  in  an  ordinary  saturated  solution  of  chromogen 
(5%  chromogen  in  distilled  water,  carefully  filtered).  The  sections  are 
left  in  this  solution  overnight,  and  the  longer  they  remain  in  it,  the  more 
marked  will  be  the  contrast,  as  far  as  stain  is  concerned,  between  the  con- 
nective and  nervous  tissues ;  then  water  is  again  twice  poured  upon  the 
sections  and  they  are  ready  for  staining.  This  process  consists  in  a 


DEVELOPMENT    OF    THE    EYE.  407 

modified  fibrin  stain  (vid.  Technic).  The  iodo-iodid  of  potassium  solu- 
tion is  the  same  (saturated  solution  of  iodin  in  a  5%  iodid  of  potassium 
solution).  Instead  of  the  customary  gentian -violet  solution,  a  hot  satu- 
rated alcoholic  (70%  to  80%  alcohol)  solution  of  methyl-violet  is  made, 
and,  after  cooling,  the  clear  portion  decanted  off;  to  every  100  c.c.  of 
this  fluid  5  c.c.  of  a  5%  aqueous  solution  of  oxalic  acid  is  added.  The 
staining  takes  place  in  a  very  short  time.  The  sections  are  then  rinsed 
and  normal  salt  solution  and  the  iodo-iodid  of  potassium  solution  poured 
over  them  (5%  iodid  of  potassium  solution  saturated  with  iodin),  and 
washed  off  with  water  and  dried  with  filter-paper  and  decolorized  in  the 
anilin  oil-xylol  solution  in  the  proportion  of  1:1.  The  reactions  are 
rapid,  and  the  thickness  of  the  section  should  not  exceed  20  /*.  This 
method  is  best  adapted  to  the  central  nervous  system  of  the  human  adult ; 
it  has  as  yet  not  been  sufficiently  tested  for  other  vertebrates. 


VIII.  THE    EYE. 

A.  GENERAL  STRUCTURE. 

THE  organ  of  vision  consists  of  the  eyeball,  or  bulbus  oculi, 
and  the  entering  optic  nerve. 

In  the  eyeball  we  distinguish  three  tunics  :  (i)  a  dense  external 
coat,  the  tunica  fibrosa  or  externa,  which  may  be  regarded  as  a 
continuation  of  the  dura  mater,  consisting  of  an  anterior  transparent 
structure,  called  the  cornea,  and  the  remaining  portion,  known  as 
the  tunica  sclerotica,  or,  briefly,  the  sclera ;  (2)  within  the  tunica 
fibrosa  a  vascular  tunic,  the  tunica  vasculosa  or  media,  subdivided 
into  the  choroid,  ciliary  body,  and  iris  ;  (3)  an  inner  coat,  the  tunica 
interna,  which  consists  of  two  layers,  the  inner  being  the  retina ; 
the  outer,  the  pigment  membrane.  The  latter  lines  the  internal 
surface  of  the  tunica  vasculosa  throughout.  Within  the  eyeball 
are  the  aqueous  humor,  the  lens,  and  the  vitreous  body.  The  lens  is 
attached  to  the  ciliary  body  by  a  special  accessory  apparatus — the 
zonula  ciliaris.  These  two  structures — the  lens  and  its  fixation 
apparatus — divide  the  cavity  of  the  eyeball  into  two  principal  cham- 
bers, the  one  containing  the  aqueous  humor  and  the  other  the 
vitreous.  The  former  is  further  subdivided  by  the  iris  into  an 
anterior  and  a  posterior  chamber.  During  life  the  latter  is  only  a 
narrow  capillary  cleft. 


B.  DEVELOPMENT  OF  THE  EYE. 

In  man  the  eyes  begin  to  develop  during  the  fourth  week  of 
embryonic  life,  and  at  first  consist  of  a  pair  of  ventrolateral  diver- 
ticula,  projecting  from  the  anterior  brain  vesicle.  These  evaginations 
gradually  push  outward  toward  the  ectoderm,  and  are  then  known 
as  the  primary  optic  vesicles.  The  slender  commissural  segments 


408 


THE    EYE. 


connecting  the  vesicles  with  the  developing  brain  are  termed  the 
optic  stalks. 

Very  soon  a  process  of  invagination  takes  place ;  that  portion 
of  the  vesicular  wall  nearest  the  ectoderm  is  pushed  inward,  thus 
forming  a  double-walled  cup — the  secondary  optic  vesicle,  or  optic 
cup.  An  internal  and  an  external  wall  may  now  be  differentiated, 
continuous  at  the  margin  of  the  cup.  At  the  same  time  a  disc-like 
thickening  of  the  adjacent  ectoderm  sinks  inward  toward  the  mouth 
of  the  cup-shaped  optic  vesicle,  forming  the  first  trace  of  the  lens. 

During  the  development  of  the  secondary  optic  vesicle  a  groove 


Blood-vessels  Sphincter 

Vein.  Canal  of  Petit,  of  the  iris.  Cornea,  pupillae.  Iris. 


Fontana's  spaces. 


Ciliary 
pro- 
cesses. 
Post,  con- 
junctival 
vessels. 
Anterior  — 
ciliary       /i 


tralis  ret- 

inae.          I 


—  Pigment 
i         layer. 

\—  a 

\-b 

I— Sclent. 

1    Choroid. 


-'--  Rectus 
.//     muscle. 

yiAdipose 
'     tissue. 


Physiologic  excavation. 


Macula  lutea. 


Fig.  329. — Schematic  diagram  of  the  eye  (after  Leber  and  Flemming)  :  a,  Vena  vorti- 
cosa  ;  £,  choroid;  /,  lens. 


is  formed  on  its  ventral  side,  extending  from  the  marginal  ring  into 
the  optic  stalk.  This  is  the  embryonic  optic  fissure,  or  the  choroi- 
dal  fissure.  At  the  edges  of  the  groove  the  two  layers  of  the  optic 
cup  are  continuous.  This  groove  serves  for  the  penetration  of 
mesoblastic  tissue  and  blood-vessels  into  the  interior  of  the  optic 
cup,  and  in  its  wall  the  fibers  of  the  optic  nerve  develop. 

The  outer  layer  of  the  secondary  optic  vesicle  becomes  the^- 
ment  membrane  ;  the  inner,  the  retina.  The  optic  nerve-fibers  con- 
sist not  only  of  the  centripetal  neuraxes  of  certain  ganglion  cells  in 


TUNICA    FIBROSA    OCULI.  409 

the  retina,  but  also  of  centrifugal  neuraxes,  which  pass   out  from 
the  brain  (Froriep). 

The  invaginating  ectoderm  which  later  constitutes  the  lens  is 
constricted  off  from  the  remaining  ectoderm  in  the  shape  of  a  vesi- 
cle, the  mesial  half  of  which  forms  the  lens  fibers  by  a  longitudinal 
growth  of  its  cells,  while  the  lateral  portion  forms  the  thin  anterior 
epithelial  capsule  of  the  lens.  The  epithelium  of  the  ectoderm 
external  to  the  lens  differentiates  later  into  the  external  epithelium 
of  the  cornea  and  conjunctiva,  neither  of  which  structures  is  at 
this  stage  sharply  defined  from  the  remaining  ectoderm.  It  is  only 
during  the  development  of  the  eyelids  that  a  distinct  demarcation 
is  established.  All  the  remaining  portions  of  the  eye,  as  the  vitre- 
ous body,  the  vascular  tunic  with  the  iris,  the  sclera  with  the 
substantia  propria  of  the  cornea  and  the  cells  of  Descemet's  layer, 
are  products  of  the  mesoderm. 


C  TUNICA   FIBROSA  OCULL 

J.  THE  SCLERA, 

The  sclera  is  the  dense  fibrous  tissue  covering  of  the  eyeball, 
and  is  directly  continuous  with  the  transparent  cornea.  At  the  poste- 
rior mesial  portion  of  the  eyeball,  the  sclera  is  perforated  for  the  en- 
trance of  the  optic  nerve,  this  region  being  known  as  the  lamina 
cribrosa.  The  sclera  consists  of  bundles  of  connective-tissue  fibers 
arranged  in  equatorial  and  meridional  layers.  At  the  external 
scleral  sulcus,  in  the  vicinity  of  the  cornea,  the  arrangement  of  the 
fibers  is  principally  equatorial.  The  tendons  of  the  ocular  muscles 
are  continuous  with  the  scleral  fibers  in  such  a  manner  that  those 
of  the  straight  muscles  fuse  with  the  meridional  fibers,  while  those 
of  the  oblique  muscles  are  continuous  with  the  equatorial  fibers. 
In  the  sclera  are  many  lymph-channels  communicating  with  those 
of  the  cornea.  They  are  much  coarser  and  more  irregularly  arranged 
than  those  of  the  cornea,  and  in  this  respect  simulate  the  lymph- 
channels  found  in  aponeuroses.  Pigmentation  is  constantly  present 
at  the  corneal  margin,  in  the  vicinity  of  the  optic  nerve  entrance, 
and  also  on  the  surface  next  the  choroid.  The  innermost  pigment 
layer  of  the  sclera  is  lined  by  a  layer  of  flattened  endothelial  cells, 
and  is  regarded  by  some  as  a  separate  membrane,  known  as  the 
lamina  fusca.  The  external  surface  of  the  sclera  also  presents  a 
layer  of  flattened  endothelial  cells,  belonging  to  the  capsule  of  Tenon, 
Anteriorly,  the  mobile  scleral  conjunctiva  is  attached  to  the  sclera 
by  a  loose  connective  tissue  containing  elastic  fibers. 

The  cornea  is  inserted  into  the  sclera  very  much  as  a  watch- 
crystal  is  fitted  into  its  frame.  At  the  sclerocorneal  junction  is 
found  an  annular  venous  sinus,  the  canal  of  Schlemm,  which  may 
appear  as  a  single  canal  or  as  several  canals  separated  by  incom- 
plete fibrous  septa.  Anteriorly  and  externally  this  canal  is  bounded 


THE    EYE. 


by  the  cornea  and  sclera ;  internally,  it  is  partly  bounded  by  the 
origin  of  the  ciliary  muscle.  The  sclera  comprises,  therefore,  one- 
half  of  the  canal-wall,  and  presents  a  corresponding  circular  sulcus, 
the  so-called  inner  scleral  sulcus. 

The  blood-vessels  of  the  sclera  are  derived  from  the  anterior 
ciliary  vessels.  The  capillaries  enter  either  into  the  ciliary  veins  or 
into  the  vense  vorticosae.  The  numerous  remaining  vessels  traverse 
the  sclera,  extending  to  the  choroid,  iris,  or  scleral  margin.  At  the 
corneal  margin  the  capillaries  form  loops. 


Cornea! 
epithelium. 


Basal  cells. 

Anterior 
elastic 
membrane. 


Substantia 
propria. 


2*  THE  CORNEA. 

The  cornea  is  made  up  of  the  following  layers  :  (i)  the  ante- 
rior or  corneal  epithelium  ;  (2)  the  anterior  elastic  membrane,  or 
Bowman's  membrane  ;  (3)  the  ground-substance  of  the  cornea,  or 

substantia  propria  ;  (4)  Des- 
cemet's  membrane  ;  (5)  the 
endothelium  of  Descemet's 
membrane. 

At  the  center  of  the 
human  cornea  the  epithe- 
lium consists  of  from  six  to 
eight  layers  of  cells,  being 
somewhat  thicker  near  the 
corneal  margin.  Its  basilar 
surface  is  smooth  and  there 
are  no  connective-tissue  pa- 
pillae. The  basal  epithelial 
layer  is  composed  of  cylin- 
dric  cells  of  irregular  height ; 
the  following  layers  contain 
irregular  polygonal  cells, 
while  the  two  or  three  most 
superficial  layers  consist  of 

flattened  cells.  The  cells  of  the  corneal  epithelium  are  all  provided 
with  short  prickles,  which  are,  however,  very  difficult  to  demon- 
strate, and  between  are  found  lymph-canaliculi.  The  lower  surfaces 
of  the  basal  cells  also  possess  short  processes  which  penetrate  into 
the  anterior  basement  membrane. 

In  man  the  anterior  elastic  or  Bowman's  membrane  is  quite 
thick  and  apparently  homogeneous,  but  may  be  separated  into 
fibrils  by  means  of  certain  reagents.  In  structure  it  belongs  neither 
to  the  elastic  nor  to  the  white  fibrous  type  of  connective  tissue,  and 
must  be  regarded  as  forming  a  class  by  itself.  Numerous  nerve- 
fibers  penetrate  its  pores  to  enter  the  epithelium.  The  thickness 
of  this  membrane  decreases  toward  the  sclera,  and  it  finally  disap- 
pears about  I  mm.  from  the  latter. 

The    substantia    propria    consists   of   connective-tissue    fibrils 


Fig.  330. — Section  through  the  anterior  portion 
of  human  cornea  ;   X  5°°' 


TUNICA    FIBROSA    OCULI. 


411 


grouped  into  bundles  and  lamellae.  Chemically  they  do  not  differ 
from  true  connective-tissue  fibers  (Morochowetz),  but  are  doubly 
refracting.  There  are  about  sixty  lamellae  in  the  human  cornea. 
The  fibrils  composing  each  lamella  are  cemented  together  and  run 
parallel  to  one  another  as  well  as  to  the  surface  of  the  cornea,  but 
they  are  so  arranged  that  the  fibrils  of  each  lamella  cross  those  of 
the  immediately  preceding  one  at  an  angle  of  about  twelve  degrees. 
The  lamellae  themselves  are  likewise  closely  cemented  to  one 
another.  The  most  superficial  lamella,  lying  immediately  beneath 
the  anterior  elastic  membrane,  is  composed  of  finer  fibers,  the  course 
of  which  is  oblique  to  the  surface  of  the  cornea.  Between  the 
anterior  and  posterior  elastic  membranes  are  bundles  of  fibers, 
which  perforate  the  various  lamellae  of  the  cornea  and  are  conse- 
quently known  as  the  perforating  or  arcuate  fibers. 

Between  the  lamellae  are  peculiar,  flattened  cells,  possessing 
irregular  or  lamella  -  like 

processes,  the  COrneal  C0r=  Lymph-canaliculi.  Corneal  space. 

puscles  ;  these  lie  in  spe- 
cial cavities  in  the  ground 
substance  of  the  substan- 
tia  .  propria,  which  are 
known  as  corneal  spaces. 
By  means  of  various  meth- 
ods (vid.  T.  3 19  and  320), 
these  corneal  spaces  may 
be  shown  to  be  part  of 
a  complicated  lymphatic 
system,  comparable  to  the 
lymph-canalicular  system 
of  fibrous  connective  tis- 
sue. This  system  of  can- 
als is  also  in  communica- 
tion with  the  lymph-chan- 
nels at  the  corneal  margin. 

The  posterior  elastic  or  Descemet's  membrane  is  not  so  inti- 
mately connected  with  the  substantia  propria  as  Bowman's  mem- 
brane. It  is  thinnest  at  the  center  of  the  cornea,  and  becomes 
thicker  toward  the  margin.  It  may  be  separated  into  finer  lamellae, 
is  very  elastic,  resists  acids  and  alkalies,  but  is  digested  by  trypsin. 

The  endothelium  of  Descemet's  membrane  consists  of  low,  quite 
regular,  hexagonal  cells,  which  in  certain  vertebrates  (dove,  duck, 
rabbit)  are  peculiar  in  that  a  fibrillar  structure  may  be  seen  in  that 
portion  of  each  cell  nearest  the  posterior  elastic  membrane.  By 
means  of  these  fibers,  not  only  adjacent  cells,  but  also  those  further 
apart,  are  joined  together.  Thus  we  have  here  to  a  marked  degree 
the  formation  of  fibers  which  penetrate  the  cells  and  connect  them 
with  one  another,  conditions  already  met  with  in  the  prickle-cells 
of  the  epidermis.  (Fig.  288.) 


Fig.  331. — Corneal  spaces  of  a  dog  ;  X  640 
(Technic  No.  320). 


412  THE    EYE. 

The  cornea  is  nonvascular.  In  fetal  life,  however,  the  capil- 
laries from  the  anterior  ciliary  arteries  form  a  precorneal  vascular 
network  immediately  beneath  the  epithelium,  a  structure  which  is 
obliterated  shortly  before  birth  and  only  rarely  seen  in  the  new- 
born. Its  remains  are  found  at  the  corneal  limbus  either  as  an 
episcleral  or  conjunctival  network  of  marginal  capillary  loops.  Fine 
branches  of  the  anterior  ciliary  arteries  extend  superficially  along 
the  sclera  to  the  corneal  margin,  and  form  here  a  network  of  capil- 
laries also  ending  in  loops,  from  which  numerous  veins  arise,  con- 
stituting a  corresponding  network  emptying  into  the  anterior  ciliary 
veins.  The  conjunctival  vessels  likewise  form  a  network  of  mar- 
ginal loops  at  the  corneal  limbus,  and  are  connected  with  the  epi- 
scleral vessels  (Leber).  Under  pathologic  conditions  the  cornea 
may  become  vascularized  from  the  marginal  episcleral  network. 

The  nerves  of  the  cornea  are  derived  from  the  sensory  fibers  of 
the  ciliary  nerves,  which  form  a  plexus  at  the  corneal  margin  ;  from 
this,  nonmedullated  fibers  penetrate  the  cornea  itself  and  form  two 
plexuses,  a  superficial  and  a  ground  plexus  ;  the  latter  is  distributed 
throughout  the  whole  substantia  propria  with  the  exception  of  its 
inner  third  (Ranvier,  81).  The  two  plexuses  are  connected  by 
numerous  anastomoses.  At  one  time  it  was  supposed  that  direct 
communication  existed  between  the  corneal  corpuscles  and  the  nerve- 
fibers  of  both  plexuses.  This  view,  however,  contradicts  the  gen- 
erally accepted  neurone  theory. 

Nerve-fibers  from  the  superficial  plexus  pass  through  the  ante- 
rior elastic  membrane  and  form  a  plexus  over  the  posterior  surface 
of  the  epithelium,  known  as  the  sub  epithelial  plexus.  From  the  lat- 
ter nerve-fibers  extend  between  the  epithelial  cells,  terminating  in 
telodendria  with  long  slender  nerve-fibrils,  which  end  in  small 
nodules.  Many  of  the  fibrils  reach  almost  to  the  surface  of  the  epi- 
thelium (Rollett,  71;  Ranvier,  81). 


D.  THE  VASCULAR  TUNIC  OF  THE  EYE. 

THE  CHOROID,  THE  CILIARY  BODY,  AND  THE  IRIS. 

From  without  inward  the  following  layers  may  be  differentiated 
in  the  choroid  :  (i)  the  lamina  stiprachoroidea  ;  (2)  the  lamina  vas- 
culosa  Halleri;  (3)  the  lamina  choriocapillaris  ;  and  (3)  the  glassy 
layer,  or  vitreous  membrane. 

The  lamina  suprachoroidea  consists  of  a  number  of  loosely 
arranged,  branching  and  anastomosing  bundles  and  lamellae  of 
fibrous  tissue,  joined  directly  to  the  lamina  fusca  of  the  sclera. 
These  bundles  and  lamellae  consist  of  white  fibrous  connective  tissue 
containing  numerous  elastic  fibers,  among  which  a  few  connective- 
tissue  cells  are  distributed.  Pigment  cells  are  also  present  in  varying 
numbers.  The  bundles  and  lamellae  are  covered  by  endothelial 


THE    VASCULAR    TUNIC    OF    THE    EYE. 


413 


cells,  and  the  spaces  and  clefts  between  them,  and  between  the 
lamina  suprachoroidea  and  the  lamina  fusca,  constitute  a  system  of 
lymph-channels — the  pericJwroidal  lymph-spaces. 

The  lamina  vasculosa  of  the  choroid  is  also  composed  of  simi- 
lar lamellae,  which,  however,  are  more  closely  arranged.  The  blood- 
vessels constitute  the  principal  portion  of  this  layer,  the  vessels 
being  of  considerable  caliber,  not  capillaries.  They  are  so  distrib- 
uted that  the  larger  vessels,  the  veins,  occupy  the  outer  layer  of 
the  lamina  vasculosa.  The  venous  vessels  converge  toward  four 
points  of  the  eyeball,  forming  at  the  center  of  each  quadrant  one 
of  the  four  vence  vorticosce.  The  arteries,  on  the  other  hand,  describe 
a  more  meridional  course. 

In  the  inner  portion  of  this  layer  is  found  a  narrow  zone, — in 
the  human  eye  only  about  10  //  in  thickness, — consisting  largely 


-  tf  ;  --  -   •  -  --^^^^^^^^^^^rsf^ 

^^^^^^^^^^^    ;  5 


Sclera.  < 


Lamina    supra-  ._)^P^^ 
choroidea. 


Lamina   vascu-  _. 
losa  Halleri. 


Lamina  chorio-  f:.-'r'>':-v"~'*'*'<£*  ••'  --•""  *""-  -_.  .-  "-  *^'-*^«fl?-U;'' 
capillaris.  ----fgi^g^J^^^^^^^^^^^^l^ 
Glassy  layer.  . —  l^^^^frBTff^iff 


Fig-  332- — Section  through  the  human  choroid  ; 


of  elastic  fibers  and  free  from  pigment  cells,  known  as  the  boundary 
zone.  This  zone  is  somewhat  thicker  in  many  mammals,  and  in 
some  of  these  presents  a  characteristic  structure.  In  the  eyes  of 
ruminants  and  horses  this  zone  consists  of  several  layers  of  con- 
nective-tissue bundles,  and  is  known  as  the  tapetum  fibrosum.  It 
gives  the  peculiar  luster  often  seen  in  the  eyes  of  these  animals.  In 
the  eyes  of  carnivora  this  zone  consists  of  several  layers  of  endothe- 
lioid  cells,  containing  in  their  protoplasm  numerous  small  crystals 
and  forming  the  iridescent  layer  known  as  the  tapetum  cellulosum. 

The  lamina  choriocapillaris  contains  no  pigment  and  consists 
principally  of  capillary  vessels,  which  form  an  especially  dense  net- 
work in  the  neighborhood  of  the  macula  lutea.  As  the  venous  cap- 
illaries become  confluent  and  form  smaller  veins,  the  latter  arrange 


THE    EYE. 

themselves  in  long,  radially  directed  networks,  and  form  in  this  way 
the  more  or  less  pronounced  stellulce  vasculosce  (Winslowii). 

The  vitreous  or  glassy  membrane  is  a  very  thin  (2  //)  homo- 
geneous membrane  which  shows  on  its  outer  surface  the  impressions 
of  the  vessels  composing  the  lamina  choriocapillaris,  and  on  its 
inner  surface  those  of  the  pigment  epithelium  of  the  retina. 

At  the  ora  serrata  the  choroid  changes  in  character ;  from  this 
region  forward,  the  choroidal  tissue  assumes  more  the  appearance  of 
ordinary  connective  tissue,  and  the  choriocapillary  layer  is  wanting. 

The  region  of  the  vascular  coat  extending  from  the  ora  serrata 
to  the  base  of  the  iris  is  known  as  the  ciliary  body.  Its  posterior 
portion,  about  4  mm.  broad,  the  orbiculus  ciliaris,  is  slightly  thicker 
than  the  choroid,  and  presents  on  its  inner  surface  numerous  small 
folds,  meridionally  placed,  consisting  of  connective  tissue  and  blood- 
vessels: Anterior  to  the  orbiculus  ciliaris  the  ciliary  body  is  thick- 
ened by  a  development  of  nonstriated  muscle — the  ciliary  muscle 
(see  below) ;  and  on  the  inner  surface  of  this  annular  thickening  are 
placed  about  seventy  triangular  folds,  meridionally  arranged — the 
ciliary  processes.  The  attached  border  of  these  processes  measures 
from  2  to  3  mm.  .  The  anterior  border  attains  a  height  of  about 
I  mm.  On  and  between  these  folds  are  found  numerous  small 
secondary  folds  or  processes  of  irregular  shape.  The  ciliary  pro- 
cesses consist  of  fibrous  connective  tissue  and  numerous  smaller 
and  larger  vessels,  which  have  in  the  main  a  meridional  arrange- 
ment. The  vitreous  membrane  extends  over  the  ciliary  body,  attain- 
ing in  the  region  of  the  ciliary  processes  a  thickness  of  3  p.  or  4  p.. 
Internal  to  the  vitreous  membrane,  the  ciliary  body  is  covered  by 
a  double  layer  of  epithelial  cells,  the  continuation  forward  of  the 
retina  (pars  ciliaris  retince).  Of  these,  the  outer  layer  is  composed 
of  cells,  which  are  deeply  pigmented,  and  are  of  cubic  or  short 
columnar  shape,  and  derived  from  the  outer  layer  of  the  secondary 
optic  vesicle,  while  the  cells  of  the  inner  layer  are  nonpigmented 
and  of  columnar  shape,  and  are  developed  from  the  inner  layer  of 
the  secondary  optic  vesicle.  In  the  region  of  the  ciliary  processes 
their  epithelial  lining  presents  here  and  there  evaginations  of  glan- 
dular appearance,  lined  by  the  unpigmented  cells.  These  evagina- 
tions are  known  as  ciliary  glands,  and  to  them  is  attributed — in 
part,  at  least — the  secretion  of  the  fluid  found  in  the  anterior  cham- 
ber of  the  eye. 

The  ciliary  muscle  is  bounded  anteriorly  (toward  the  anterior 
chamber)  by  the  ligamentum  pectinatum  iridis,  externally  by  the 
cornea  and  sclera,  posteriorly  by  the  orbiculus  ciliaris,  and  inter- 
nally by  the  ciliary  processes.  It  consists  of  nonstriated  muscle- 
fibers  in  the  majority  of  vertebrates.  This  muscle  is  divided  into 
three  portions.  The  outer  or  meridional  division  extends  from  the 
posterior  elastic  lamina  of  the  cornea  and  its  continuation,  forming 
the  inner  wall  of  the  sinus  venosus  sclerae,  to  the  posterior  portion 
of  the  ciliary  ring.  The  origin  of  the  middle  division  is  identical  with 


THE  VASCULAR  TUNIC  OF  THE  EYE. 


415 


that  of  the  outer,  but  its  fibers  (assuming  that  we  have  before  us  a 
meridional  section)  spread  out  like  a  fan,  and  occupy  a  large  area 
at  their  insertion  into  the  ciliary  ring  and  ciliary  processes.  The 
radial  course  of  these  fibers  is  interrupted  by  circular  bundles.  The 
third  or  inner  division  (^fibrce  circulares,  fibers  of  Mullet')  is  situated 
between  the  ligamentum  pectinatum,  the  ciliary  processes,  and  the 
middle  portion  of  the  muscle  just  mentioned,  and  is  thus  near  the 
base  of  the  iris. 

Between  the  ciliary  muscle  and  the  posterior  elastic  membrane 
of  the  cornea  is  an  intermediate,  richly  cellular  tissue,  which  maybe 
regarded  as  a  continuation  of  this  elastic  membrane,  and  which 
forms  a  part  of  the  wall  of  the  sinus  venosus.  Another  structure 
internal  to  the  foregoing  and  directed  posteriorly  is  the  ligamentum 
pectinatum  iridis,  which  encircles  the  anterior  chamber  and  is  a  con- 
tinuation of  Descemet's  membrane  to  the  base  of  the  iris.  It  con- 


Corneal  epithe- 
lium. 

Substantia  pro- 
pria. 


Loose  connec- 
tive tissue  of 
the  conjunc- 
tiva. 


Conjunctiva. 


Iris. 
Pigment  layer. 


Meridional  fibers. 
Radial  fibers. 
Miiller's  fibers. 


Sclera.  Processus  ciliares. 

Fig.  333. — Meridional  section  of  the  human  ciliary  body ;  X  2O- 


sists  of  fibers  and  lamellae  lined  by  endothelial  cells,  and  bounds 
certain  intercommunicating  spaces  lying  in  the  ligament,  known  as 
the  spaces  of  Fontana.  The  latter  communicate  on  the  one  side 
with  the  perivascular  spaces  of  the  sinus  venosus  sclerae  (canal  of 
Schlemm),  and  on  the  other  with  the  anterior  chamber. 

The  iris  must  be  looked  upon  as  a  continuation  of  the  choroid, 
the  vitreous  layer  of  which  is  directly  continuous  with  the  posterior 
vitreous  lamella  of  the  iris,  or  Bruch's  membrane.  The  iris  is  also 
connected  at  its  anterior  peripheral  portion  with  the  ligamentum 
pectinatum. 

The  iris  possesses  the  following  layers,  beginning  anteriorly  : 
(i)  the  anterior  endothelium  ;  (2)  the  ground-layer,  or  stroma  of 
iris,  together  with  the  sphincter  muscle  of  the  pupil  ;  (3)  the  pos- 
terior vitreous  layer,  or  the  membrane  of  Bruch  ;  and  (4)  the  two- 
layered,  pigmented  epithelium — the  pars  iridica  retinae. 


416  THE    EYE. 

The  anterior  endothelium  is  a  single  layer  of  irregularly  polyg- 
onal, nonpigmented  cells,  and  is  directly  continuous  with  the 
endothelium  of  the  pectinate  ligament. 

The  ground-layer  or  stroma  of  iris  consists  anteriorly  of  a  fine 
reticulate  tissue  rich  in  cellular  elements  (reticulate  layer).  The 
remaining  strata  which  form  the  bulk  of  the  ground-layer  consti- 
tute its  vascular  layer.  The  vessels  are  here  peculiar  in  that  they 
are  covered  by  coarse,  circular,  connective -tissue  fibers  forming  vas- 
cular sheaths.  There  is  also  an  entire  absence  of  muscular  tissue 
in  the  vessel  walls.  The  nerves,  too,  are  enveloped  by  a  dense  con- 
nective tissue.  In  all  eyes  (except  the  albinotic)  pigment  is  found 
in  the  connective  tissue. 

On  the  posterior  inner  surface  of  the  ground-layer  is  a  band  of 
smooth  muscle-fibers  encircling  the  pupil — the  sphincter  muscle  of 
the  pupil. 

The  membrane  of  Bruch  is  a  structureless  hyaline  sheath.  At 
its  anterior  surface  and  closely  connected  with  it  is  a  layer  of  spin- 
dle-shaped cells  having  a  radial  arrangement  and  containing  pig- 
ment. Closer  microscopic  inspection  reveals  the  fact  that  in  all 
probability  these  elements  represent  muscular  tissue.  Here,  there- 
fore, we  have  to  deal  with  a  dilator  muscle  of  the  pupil. 

The  posterior  epithelium  is  the  direct  continuation  of  the  two 
epithelial  layers  of  the  ciliary  body,  and  represents  the  anterior  por- 
tion of  the  secondary  optic  vesicle,  the  two  layers  being  continuous 
at  the  margin  of  the  pupil.  In  the  iris  both  layers  of  cells  are  pig- 
mented.  (Compare  Retzius,  93.) 

The  arteries  of  the  choroid  are  derived  from  the  short  poste- 
rior ciliary,  the  long  ciliary,  and  the  anterior  ciliary  arteries.  The 
short  posterior  ciliary  arteries  penetrate  the  sclera  in  the  vicinity  of 
the  optic  nerve,  mingle  with  the  retinal  vessels,  and  spread  through 
the  choroid,  where  they  form  the  choriocapillary  layer.  The  long 
posterior  ciliary  arteries  (a  mesial  and  a  lateral)  penetrate  the  sclera 
and  course  forward  between  choroid  and  sclera  to  the  ciliary  body, 
forming  there  the  circulus  arteriosus  iridis  major ;  they  also  supply 
the  ciliary  muscle,  the  ciliary  processes,  and  the  iris,  and  anasto- 
mose in  the  ciliary  ring  with  the  branches  of  the  short  posterior 
and  anterior  ciliary  arteries.  The  latter  lie  beside  and  partly 
within  the  straight  ocular  muscles,  penetrating  the  latter  at  the  an- 
terior margin  of  the  sclera  ;  they  give  off  branches  to  the  circulus 
arteriosus  iridis  major  and  to  the  ciliary  muscles,  anastomosing  at 
the  same  time  with  the  posterior  ciliary  arteries.  (Compare  Figs. 
329  and  334.)  Within  the  iris  the  blood-vessels  generally  take 
a  radial  direction,  but  also  anastomose  with  one  another,  forming 
capillaries,  and  subsequently  the  circulus  arteriosus  iridis  minor  at 
the  inner  pupillary  margin.  From  the  region  supplied  by  the 
posterior  ciliary  arteries  most  of  the  blood  is  carried  toward  the 
vorticose  veins.  The  anterior  ciliary  veins  convey  the  blood  com- 
ing from  the  arteries  of  the  same  name.  Into  these  veins  is  also 


THE    VASCULAR    TUNIC    OF    THE    EYE. 


417 


Margin  of 
pupil. 


poured  the  blood  from  the  veins  lying  in  the  canal  of  Schlemm, 
the  canal  itself  being  in  reality  an  open  venous  sinus.  Besides  this, 
these  veins  convey  also  venous  blood  from  the  conjunctiva  (Leber). 
The  nonstriated  muscle  of  the  ciliary  body  and  iris  receives  its 
innervation  through  sympathetic  nerve-fibers,  neuraxes  of  sympa- 
thetic neurones,  the  cell- bodies  of  which  are  situated  either  in  the 
ciliary  ganglia  or  in  the  superior  cervical  ganglia.  The  neuraxes  of 
the  sympathetic  cells  forming  the  ciliary  ganglia  form  the  short 
ciliary  nerves,  which  pierce 
the  sclera  in  the  neighbor- 
hood of  the  optic  nerve  and 
pass  forward,  to  terminate  in 
the  muscle  of  the  ciliary  body 
and  the  sphincter  muscle  of 
the  pupil.  Stimulation  of 
these  nerves  causes  a  con- 
traction of  the  ciliary  muscle 
and  a  closure  of  the  pupil. 
The  cell-bodies  of  the  sympa- 
thetic neurones  forming  the 
ciliary  ganglia  are  surrounded 
by  pericellular  plexuses,  the 
terminations  of  small  medul- 
lated  nerve-fibers  (white  rami 
fibers)  which  reach  the  ciliary 
ganglia  through  the  oculo- 
motor nerves.  Neuraxes  of 
sympathetic  neurones,  the 
cell-bodies  of  which  are  sit- 
uated in  the  superior  cervical 
ganglia,  reach  the  eye  through 

the  cavernous  plexuses,  to  ter-  Fig.  334.— Injected  blood- vessels  of  the  human 
minate,  it  is  thought, — in  part,  choroid  and  iris;  x  7- 

at  least, — in  the  dilator  of  the 

iris,  since  stimulation  of  these  nerves  causes  a  dilatation  of  the 
pupils.  The  cell-bodies  of  these  sympathetic  neurones  are  sur- 
rounded by  pericellular  plexuses,  the  terminations  of  white  rami 
fibers  which  leave  the  spinal  cord  through  the  first,  second,  and 
third  thoracic  nerves  (Langley),  and  which  reach  the  superior  cer- 
vical ganglia  through  the  cervical  sympathetic. 

Melkirch  and  Agababow  have  shown  that  numerous  sensory 
nerves  terminate  in  free  sensory  endings  in  the  connective  tissue 
of  the  ciliary  body  and  iris.  The  sensory  nerve-supply  of  the  iris 
is  especially  rich. 


Choroid. 


27 


4i8 


THE    EYE. 


E*  THE  INTERNAL  OR  NERVOUS  TUNIC  OF 
THE  EYE. 

This  tunic  is  composed  of  two  layers  :  the  outer,  or  stratum  pig- 
menti  ;  and  the  inner,  or  retina. 

J.  THE  PIGMENT  LAYER. 

The  pigment  layer  develops,  as  we  have  seen,  from  the  outer 
layer  of  the  secondary  optic  vesicle.  It  consists  of  regular  hexa- 
gonal cells,  12  n  to  1 8  fi  in  length  and  9  p.  in  breadth,  which  con- 
tain black  pigment  in  the  form  of  granules.  The  inner  surfaces 
of  these  cells  possess  long,  thread-like  and  fringe-like  processes, 
between  which  project  the  external  segments  of  the  rods  and  cones 
of  the  retina,  yet  to  be  described.  The  nuclei  of  the  pigment  cells 
lie  in  the  outer  ends  of  the  cells,  the  so-called  basal  plates,  and  are 
not  pigmented.  The  distribution  of  the  pigment  varies  according  to 
the  illumination  of  the  retina.  If  the  latter  be  darkened,  the  pig- 
ment collects  at  the  outer  portion  of  each  cell ;  if  illuminated,  the 
pigment  is  evenly  distributed  throughout  the  whole  cell.  The  pig- 
ment granules  are  therefore  mobile  (Kiihne,  79). 

2.  THE  RETINA. 

The  retina  has  not  the  same  structure  throughout.  In  certain 
areas  peculiarities  are  noticeable  which  must  be  described  in  detail ; 
such  areas  are  :  (i)  the  macula  lutea ;  (2)  the  region  of  the  papilla 
(papilla  nervi  optici) ;  (3)  the  ora  serrata ;  (4)  the  pars  ciliaris 
retinae  ;  and  (5)  the  pars  iridica  retinae. 

We  shall  begin  with  the  consideration  of  that  portion  of  the 
retina  lying  between  the  ora  serrata  and  the  optic  papilla  (exclusive 
of  the  macula  lutea). 

From  without  inward,  we  differentiate:  (i)  the  layer  of  vis- 
ual cells,  including  the  outer  nuclear  layer ;  (2)  the  outer  molecu- 
lar (plexiform)  layer  ;  (3)  the  inner  nuclear  or  granular  layer  ;  (4) 
the  inner  molecular  (plexiform)  layer  ;  (5)  the  ganglion-cell  layer  ; 
(6)  the  nerve -fiber  layer.  Besides  these,  we  must  also  consider  the 
supporting  tissue  of  the  retina  and  Miiller's  fibers,  together  with  the 
internal  and  external  limiting  membranes. 

The  visual  cells  are  either  rod-visual  cells  or  cone-visual  cells. 
The  rod-visual  cells  consist  of  a  rod  and  a  rod-fiber  with  its 
nucleus.  The  rod  (40  p.  to  50  //  in  length)  consists  of  two  seg- 
ments, an  outer  and  an  inner,  the  former  of  which  is  doubly  refrac- 
tive and  may  be  separated  into  numerous  transverse  discs  by  the 
action  of  certain  reagents.  The  inner  is  less  transparent  than  the 
outer  segment,  and  its  inner  end  shows  a  fine  superficial  longitu- 
dinal striation  due  to  impressions  from  the  fiber-baskets  formed  by 
Miiller's  fibers.  In  the  lower  classes  of  vertebrates  a  rod-ellipsoid 


THE  INTERNAL  OR  NERVOUS  TUNIC  OF  THE  EYE. 


419 


(a  fibrillar  structure)  may  easily  be  demonstrated  in  the  outer  region 
of  each  inner  portion  ;  in  many  mammalia  and  in  man  the  demon- 
stration of  this  is  more  difficult.  This  structure  is  a  planoconvex, 
longitudinally  striated  body,  the  plane  surface  of  which  is  coincident 
with  the  external  surface  of  the  inner  segment,  its  inner  convex  sur- 
face lying  at  the  junction  of  the  outer  and  middle  thirds  of  the  inner 
segment.  The  rod-fibers  extend  as  far  as  the  outer  molecular  layer 
of  the  retina,  where  they  end  in  small  spheric  swellings.  The  nuclei 
of  the  rod-visual  cells  are  found  at  varying  points  within  the  rod- 
fibers,  but  rarely  close  to  the  inner  segment.  When  treated  with 
certain  fixing  agents  and  stains,  the  rod-nuclei  are  seen  to  show 
several  zones,  which  stain  alternately  light  and  dark  (striation  of  the 
rod-nuclei). 


Layer  of  nerve-    — 
fibers. 

Ganglion-cell  layer.    ^-- 


Inner  molecular 
layer. 


Inner  nuclear  layer.  — 


Outer  molecular 
layer. 


Outer  nuclear 
layer. 

Ext.  limiting  mem- 
brane. 
Inner  segment  of 

rod. 

Inner  segment  of 
cone. 

Outer  segment  of 

cone. 
Outer  segment  of 

rod. 


Fig.  335.— Section  of  the  human  retina;   X  7°°- 


The  cone-visual  cells  consist,  similarly  to  the  rod-visual  cells, 
of  a  cone  and  a  cone-fiber  with  its  nucleus.  The  cone  (15  //  to 
25  IJL  in  length)  is,  as  a  whole,  shorter  than  the  rod,  and  its  inner 
segment  is  considerably  broader  than  that  of  the  rod.  The  cone 
ellipsoid  comprises  the  outer  two-thirds  of  the  inner  segment,  and 
the  outer  segment  has  a  more  conical  shape.  The  cone-fiber  like- 
wise extends  as  far  as  the  outer  molecular  layer,  where  it  ends  in 
a  branched  basal  plate.  Its  somewhat  larger  nucleus  is  always 
found  in  the  vicinity  of  the  inner  segment  of  the  cone.  The 
inner  surfaces  of  the  inner  segments,  not  only  of  the  cone-cells,  but 
also  of  the  rod-visual  cells,  lie  in  one  plane,  corresponding  to  the 


420 


THE    EYE. 


external  limiting  membrane,  a  structure  composed  of  the  sustenta- 
cular  fibers  of  Muller.  The  rod-fibers  and  cone-fibers,  with  the 
nuclei  of  the  rod-  and  cone-visual  cells,  lie  between  the  external 
limiting  membrane  and  the  outer  molecular  layer.  It  will  be 
observed,  therefore,  that  the  visual  cells  include  the  layer  of  rods 
and  cones  and  the  outer  nuclear  layer. 

The  outer  molecular  layer  consists  :  (i)  of  the  ramifications  of 
Miiller's  fibers  ;  (2)  of  the  knob  and  tuft-like  endings  of  the  visual 
cells  ;  and  (3)  of  the  dendritic  processes  of  the  bipolar  cells  of 
the  inner  nuclear  layer.  These  structures  will  be  considered  more 
in  detail  in  discussing  the  relations  of  the  elements  comprising  the 
retina. 

The  inner  nuclear  layer  contains:  (i)  the  nucleated  stratum 
of  Miiller's  sustentacular  fibers  ;  (2)  ganglion  cells  situated  in  the 
outer  region  of  the  layer  and  extending  in  a  horizontal  direction  ; 
(3)  bipolar  ganglion  cells  with  oval  nuclei,  densely  placed  at  various 
depths  of  the  layer  and  vertical  to  it ;  (4)  amacrine  cells  (neurones, 
apparently  without  neuraxes)  lying  close  to  the  inner  margin  of 
the  layer  and  forming  with  their  larger  nuclei  a  nearly  continuous 
layer  of  so-called  spongioblasts.  The  numerous  processes  of  these 
spongioblasts  lie  in  the  inner  molecular  layer,  the  composition  of 
which  will  be  further  discussed  later. 

The  ganglion-cell  layer  of  the  optic  nerve  consists,  aside  from 
centrifugal  neuraxes  and  the  fibers  .of  Muller,  which  are  here 
present,  of  multipolar  ganglion  cells,  the  dendrites  of  which  extend 
outward  and  the  neuraxes  of  which  are  directed  toward  the  optic 
nerve-fiber  layer.  These  cells  vary  in  size,  and  their  nuclei  are 
typical,  being  relatively  large,  deficient  in  chromatin,  and  always 
provided  with  large,  distinct  nucleoli.  In  man  the  optic  nerve- 
fibers  of  the  retina  are  nonmedullated. 

All  these  structures  are  typical  of  that  portion  of  the  retina 
lying  behind  the  ora  serrata.  The  retina  in  the  vicinity  of  the  optic 
papilla  and  macula  lutea  must  be  taken  up  separately. 

3.  REGION  OF  THE  OPTIC  PAPILLA. 

The  optic  papilla  is  the  point  of  entrance  of  the  optic  nerve 
into  the  retina.  At  the  center  of  the  papilla,  in  the  region  where 
the  nerve-fibers  spread  out  radially  in  order  to  supply  the  various 
areas  of  the  retina,  is  a  small,  funnel-shaped  depression,  the  physi- 
ologic excavation.  The  fibers  of  the  optic  nerve  lose  their  medullary 
sheaths  during  their  passage  through  the  sclera  and  choroid,  and  then 
continue,  penetrating  the  various  layers  of  the  retina,  to  the  inner 
surface  of  the  latter,  over  which  they  spread  in  a  layer  which  grad- 
ually becomes  thinner  toward  the  ora  serrata.  On  account  of  the  de- 
flection of  the  nerve-fibers,  and  because,  during  their  passage  through 
the  sclera,  they  lose  their  medullary  sheaths  at  one  and  the  same 
point,  the  optic  nerve  becomes  suddenly  thinner.  The  result  is  a 


THE    INTERNAL    OR    NERVOUS    TUNIC    OF    THE    EYE. 


421 


deeply  indented  circular  depression  in  this  region.  On  this  depres- 
sion border  the  three  ocular  tunics.  At  this  point  the  retina  is 
interrupted,  the  outer  layers  extending  to  the  bottom  of  the  de- 
pression, while  the  inner  cease  at  its  margin.  In  many  cases  the 
outer  layers  of  the  retina  are  separated  from  the  optic  nerve  by  a  thin 
lamina  of  supporting  tissue  (intermediate  tissue). 


L 


Lamina  cribrosa. 


—Sclera. 

,,'Pigment  layer. 
",-Rods  and  cones. 

Outer  nuclear  layer. 

Outer  molecular  layer. 

Inner  nuclear  layer. 

Inner  molecular  layer. 

Layer  of  nerve-fibers. 


Physiologic  excavation. 


Fig.  336.  —  Section  through  point  of  entrance  of  human  optic  nerve  ;  X  4°- 


4,  REGION  OF  THE  MACULA  LUTEA. 

At  the  center  of  the  macula  lutea  is  a  trough-like  depression, 
the  fovea  centralis,  the  deepest  part  of  which,  the  fundus,  lies  very 
close  to  the  visual  axis.  Here  the  layers  of  the  retina  are  practic- 
ally reduced  to  the  cone  -visual  cells.  The  margin  of  this  depression 
is  somewhat  thickened,  owing  to  an  increase  in  the  thickness  of  the 
nerve-fiber  and  ganglion-cell  layers.  Toward  the  fundus  of  the  fovea 


,  Fovea  centralis. 

Layer    of       ~~f '-*?'*"'  -  ^-'^ss****^  i 

nerve-fibers.     ©^  J^ 

Ganglion-cell  J  £vf!< 

layer. 

Inner  molecu-  ___" 

lar  layer.      ~ ,  aft*.,  -^> 

Inner  nuclea:  c  ->.., 

layer. 
Outer  molec-.JS| 

ular  layer.     "r?3  ?  "-«<;•  ^#B|¥**{<»* 

Outer  fibrous  H  '  c '.'\ 

layer. 

Outer  nuclear  Jfi 
layer. 

Cones.  _jp 

' 

Fig.  337- — Section  through  human  macula  lutea  and  fovea  centralis  ;  X  *5°'  As 
a  result  of  treatment  with  certain  reagents,  the  fovea  centralis  is  deeper  and  the  margin 
more  precipitous  than  during  life. 


each  of  the  four  inner  retinal  layers  becomes  reduced  in  thickness, 
the  inner  layer  first  and  the  three  others  in  their  order :  the  inner 
molecular  layer,  however,  seems  to  extend  as  far  as  the  fundus.  As 
we  have  seen,  only  the  cone-visual  cells  are  found  in  the  fovea  cen- 
tralis, there  being  an  entire  absence  of  the  rod-visual  cells.  Since 
the  nuclei  of  the  cone-visual  cells  are  in  the  immediate  neighborhood 


422 


THE    EYE. 


of  the  cones,  and  since  the  cone-fibers,  in  order  to  reach  the  outer 
molecular  layer,  must  here  describe  a  curve,  there  arises  a  peculiar 
layer,  composed  of  obliquely  directed  fibers,  known  as  the  outer 
fiber-layer.  In  other  words,  the  fibers  of  this  region  are  more  dis- 
tinctly seen  because  they  are  not  covered  by  the  rod-nuclei  and  rod- 
fibers. 

The  yellowish  color  of  the  fovea  centralis  is  due  to  pigment  held 
in  solution  within  the  layers  of  the  retina.  The  cone-visual  cells 
themselves  contain  no  pigment. 


5.  ORA  SERRATA,  PARS  CILIARIS  RETINAE,  AND  PARS  IRIDICA 

RETINAE. 

In  the  region  of  the  ora  serrata  the  retina  suddenly  becomes 
thinner.  As  seen  from  the  inner  surface  of  the  retina,  its  decrease 
presents  the  appearance  of  an  irregular  curve  rather  than  of  the 
segment  of  a  sphere.  Shortly  before  the  retina  terminates,  its  layers 
become  markedly  reduced,  certain  ones  disappearing  entirely ;  first 
the  nerve-fiber  layer,  then  the  ganglion-cell  layer  and  cone-  and  rod- 
visual  cells,  their  place  being  taken  by  an  indifferent  epithelium. 
The  inner  molecular  layer  of  the  retina  gradually  loses  the  pro- 
cesses which  penetrate  inward.  In  the  region  of  the  ora  serrata  the 
sustentacular  fibers  are  markedly  developed. 

The  pars  ciliaris  retinae  consists  essentially  of  two  simple 
layers  of  cells,  of  which  the  external  represents  the  pigment  layer 
and  the  internal  the  inner  epithelium  of  the  secondary  optic  vesicle. 
In  the  pars  iridica  retinae  the  arrangement  is  similar ;  here  both 
layers  are  pigmented. 

6.  MULLER'S  FIBERS  OF  THE  RETINA. 

Genetically,  the  sustentacular  fibers,  or  fibers  of  Miiller,  in  the 
retina  are,  like  the  whole  retina,  of  ectodermic  origin,  and  repre- 
sent a  highly  developed  form  of  neurogliar  tissue.  They  penetrate 
the  retina  from  within  and  extend  as  far  as  the  inner  segments  of 
the  rods  and  cones.  Each  fiber  represents  a  long,  greatly  modified 
epithelial  cell,  terminating  in  one  or  more  broad  basal  plates,  which 
come  in  contact  with  those  of  adjacent  fibers,  thus  forming  a  sort 
of  membrane — -the  internal  limiting  membrane.  Owing  to  its 
marked  plasticity,  each  fiber  presents  certain  peculiarities  within 
the  various  layers  of  the  retina  through  which  it  penetrates. 
Thus,  within  the  molecular  layers  the  fiber  is  provided  with  trans- 
versely directed  processes  and  platelets.  Within  the  nuclear  layers, 
on  the  other  hand,  are  numerous  lateral  indentations,  which  corre- 
spond to  the  impressions  produced  by  the  cells  of  these  layers.  At 
the  inner  surface  of  the  cones  and  rods  the  fibers  terminate  in  end- 
plates,  which  represent  cuticular  formations,  and,  blending  with  one 
another,  form  a  single  membrane — the  external  limiting  membrane. 


THE  INTERNAL  OR  NERVOUS  TUNIC  OF  THE  EVE.       423 

This  membrane  is  perforated  by  the  rod-fibers  and  cone-fibers.  The 
end-plates  of  the  fibers  give  off  externally  short,  inflexible  fibrils, 
which  form  the  fiber-baskets  containing  the  basilar  portions  of  the 
inner  segments  of  the  rods  and  cones.  (Vid.  Fig.  338.) 


7.    THE    RELATIONS  OF  THE  ELEMENTS  OF  THE  RETINA  TO 

ONE  ANOTHER. 

We  shall  now  take  up  the  relationships  existing  between  the 
various  elements  of  the  retinal  strata,  giving  the  theories  now 
generally  accepted  and  based  on  observations  made  with  the  Golgi 
and  methylene-blue  methods,  and  more  particularly  on  the  investi- 
gations of  Ramon  y  Cajal  (see  diagram,  Fig.  338) : 

1.  The  inner  processes  of  the  rod-visual  cells  end,  as  a  rule,  in 
small  expansions  within  the  outer  molecular  layer,  in  which  also  the 
processes  of  the  cone-visual  cells  terminate  in  broader  branched 
pedicles.      In  this  layer  also  are  situated  the  terminal  arborizations 
of  the  dendrites  and  neuraxes  of  certain  cells  belonging  to  the  inner 
nuclear  layer. 

2.  The  inner  nuclear  layer  consists,  as  we  have  seen,  (a)  of  bipolar 
cells,  which  constitute  the  principal  portion  of  this  layer,  (^)  of  hori- 
zontally placed  cells  lying  immediately  beneath  the  outer  molecular 
layer,  and  (c)  of  the  layer  of  spongioblasts  situated  at  the  junction 
of  the  inner  nuclear  with  the  inner  molecular  layer.     The  bipolar  cells 
comprise  the  following  :  («)  Bipolar  cells  of  the  rod-visual  cells  the 
dendrites  of  which  intertwine  around  the  basilar  portions  of  the  rod- 
visual  cells,  and  the  neuraxes  of  which  end  in  telodendria  in  the  neigh- 
borhood of  the  cell-bodies  of  the  nerve-cells  of  the  ganglion-cell  layer. 
(,5)  Bipolar  cells  of  the  cone-visual  cells.     The  dendrites  of  these  cells, 
which  also  end  in  the  outer  molecular  layer,  are  there  in  relation  to 
the  basilar  processes  of  the  cone-fibers.     Their  neuraxes  come  in 
contact,  by  means  of  terminal  arborizations,  with  the  dendrites  of  the 
ganglion  cells  of  the  ganglion-cell  layer  at  varying  depths  of  the 
inner   molecular  layer.     (^)  Besides  these,  there  are  also   bipolar 
cells  which,  as  in  the  case  of  a  and  /9,  form  contact  with  the  rod-  and 
cone-visual  cells,  but  end  on  the  cell-bodies  of  the  ganglion  cells 
of  the  ganglion-cell  layer.     The  horizontal  cells  send  their  dendrites 
into  the  outer  molecular  layer,  while  their  neuraxes  extend  hori- 
zontally and  give  off  numerous  collaterals  to  the  same  layer,  ending 
there  in  telodendria.  These  cells  are  of  two  varieties:  the  smaller,  in- 
directly connecting  the  cone-visual  cells  with  one  another  by  means 
of  their  dendrites  and  neuraxes  ;  and  the  larger,  more  deeply  situated 
cells,  connecting  in  a  similar  manner  the  basilar  ends  of  the  rod- 
visual  cells.      A   few  cells  of  the  second  variety  give   off  one  or 
two  dendrites  each,  which  penetrate  through  the  inner  nuclear  layer 
into  the  inner  molecular  layer. 

3.  The  inner  molecular  layer.     This  is  composed  of  five  strata. 
The  majority  of  the  spongioblasts  in  the  inner  nuclear  layer  send 


424 


THE    EYE. 


their  processes  upward  into  the  inner  molecular  layer,  in  which  some 
end  in  fine  arborizations  in  the  first,  others  in  the  second,  and  still 
others  in  the  third  interstice,  separating  the  strata  of  the  inner 
molecular  layer  from  one  another.  Besides  these  so-called  stratum 
spongioblasts ,  there  are  also  others  in  the  inner  nuclear  layer,  the 
diffuse  spongioblasts,  whose  ramifications  end  simultaneously  in  sev- 


eral  or  in  all  of  the  strata  of  the  inner  molecular  layer.  Besides  the 
ramifications  of  the  spongioblasts  just  mentioned,  autochthonous 
cells  are  also  present.  These  lie  in  one  of  the  interstices  of  the 
molecular  layer,  their  ramifications  spreading  out  in  a  horizontal 
direction.  Besides  all  these  structures  the  dendrites  of  the  cells 


THE    INTERNAL    OR    NERVOUS    TUNIC    OF    THE    EYE.  425 

in  the  ganglion-cell  layer  also  ramify  throughout  the  inner  molec- 
ular layer. 

4.  The  ganglion  -  cell  layer.     The   cell-bodies    are    irregularly 
oval ;   their  dendrites  extend  into  the  inner  molecular  layer,  and 
their    neuraxes     into    the    nerve-fiber    layer.      According    to    the 
manner  of  their  dendritic  termination,   the  ganglion  cells  may  be 
divided  into   three  groups  :  (i)  those  the  dendrites  of  which  ex- 
tend into  but  one  stratum  of  the  molecular  layer ;  (2)  those  the 
dendrites  of  which  extend  into  several  strata  of  the  molecular  layer  ; 
and  (3)  those  the  dendrites  of  which  are  distributed  throughout  the 
entire  thickness  of  the  molecular  layer.     Thus,  these  three  groups 
are  made   up   of  the   so-called  mono-stratified,  poly -stratified,  and 
diffuse  cells  ;  by  means  of  their  dendrites  they  come  in  contact  with 
one  or  several  of  the  neuraxes   of  the  bipolar  cells  of  the  inner 
nuclear  layer. 

5.  The  nerve-fiber  layer  of  the   retina.       This  layer  consists  of 
centripetal  neuraxes  from  the  ganglion  cells  of  the  ganglion-cell 
layer,  and  of  centrifugal  nerve -fibers  ending  in  various  layers  of 
the  retina,  including  the  outer  molecular  layer. 


8.  THE  OPTIC  NERVE. 

Within  the  orbit  the  optic  nerve  possesses  an  external  sheath, 
which  is  an  extension  of  the  dura  mater  and  is  continuous  with  the 
scleral  tissue,  and  an  inner  sheath,  which  is  a  prolongation  of  the  pia 
mater.  Between  these  two  sheaths  is  a  fissure,  divided  into  two 
smaller  clefts  by  a  continuation  of  the  arachnoid.  Both  these  clefts 
are  traversed  by  connective-tissue  trabeculae.  The  inner  cleft  com- 
municates with  the  subarachnoid  space  ;  and  the  outer  narrower 
cleft,  with  the  subdural  space. 

The  fibers  of  the  optic  nerve  are  medullated,  but  there  is  no 
neurilemma  (sheath  of  Schwann),  the  latter  being  represented  by  the 
neuroglia.  In  the  region  of  the  sclera  and  choroid  the  optic  nerve- 
fibers  lose  their  myelin,  and  the  septa  of  the  inner  or  pial  sheath 
become  better  developed  and  relatively  more  numerous.  Connec- 
tive-tissue fibers  from  the  sclera  and  choroid  also  traverse  this 
region  of  the  optic  nerve,  giving  rise  to  what  is  known  as  the 
lamina  cribrosa.  At  from  I  y2  to  2  cm.  from  the  eyeball  there  enter 
into  the  optic  nerve  laterally  and  ventrally  (according  to  J.  Deyl, 
mesially)  the  central  artery  and  vein  of  the  retina,  which  very  soon 
come  to  lie  within  the  axis  of  the  nerve.  Here  they  are  surrounded 
by  a  common  connective-tissue  sheath  which  is  in  direct  connec- 
tion with  the  perineurium.  The  optic  nerve-fibers  extend  through 
the  lamina  cribrosa  into  the  retina,  where  they  spread  out  as  the 
nerve-fiber  layer  in  the  manner  previously  described. 


426 


THE    EYE. 


-.  Vein. 


9.  BLOOD-VESSELS  OF  THE  OPTIC  NERVE  AND  RETINA, 
The  blood-vessels  of  the  optic  nerve  are  principally  derived  from 
the  vessels  of  the  pial  sheath.  In  that  portion  of  the  nerve  con- 
taining the  central  vessels  of  the 
retina  the  latter  anastomose  with 
the  pial  vessels,  so  that  this  por- 
tion of  the  optic  nerve  is  also 
supplied  by  the  central  vessels. 
At  their  entrance  through  the 
sclera  the  short  posterior  ciliary 
arteries  form  a  plexus  around  the 
optic  nerve,  the  arterial  circle  of 
Zinn,  which  communicates,  on 
the  one  hand,  with  the  vessels  of 
the  pial  sheath,  and,  on  the  other, 
with  those  of  the  optic  nerve. 
At  the  level  of  the  choroid  the 
vessels  of  the  latter  communicate 
by  means  of  capillaries  with  the 

the   human"  retina-    surface   oreDaration  :       Central  vessels  of  the  Optic  nerve. 

The  central  artery  and  vein 
of  the    retina    enter    and    leave 

the    retina   at    the    optic    papilla,    dividing    here,   or  even   within 
the  nerve  itself,  into  the  superior  and  inferior  papillary  artery  and 


-—-Artery. 


Zone  sur- 
rounding 
artery  free 
from  capil- 
laries. 


Fig.  339. — Injected  blood-vessels  of 
human    retina ;    surface   preparation ; 


' —  Vascular 
plexus  of 
macula  lutea 
with  wide 
meshes. 
Fovea  centra- 
lis,  free  from 
vessels. 


Fig-  340- — Injected  blood-vessels  of  human  macula  lutea  ;  surface  preparation  ;  X  28- 

vein.     Both   the   latter  again  divide  into  two  branches,  the  nasal 
and  temporal  arteriole  and  venule,  known,  according  to  their  posi- 


THE    VITREOUS    BODY. 

tions,  as  the  superior  and  inferior  nasal  and  temporal  artery  and 
vein. 

Besides  these  vessels,  two  small  arteries  also  arise  from  the 
trunk  of  the  central  artery  itself,  and  extend  to  the  macula.  Two 
similar  vessels  extend  toward  the  nasal  side  as  the  superior  and 
inferior  median  branches.  Within  the  retina  itself  the  larger  ves- 
sels spread  out  in  the  nerve-fiber  layer,  forming  there  a  coarsely 
meshed  capillary  network  connected  by  numerous  branches  with  a 
finer  and  more  closely  meshed  network  lying  within  the  inner 
nuclear  layer.  The  venous  capillaries  of  this  network  return  as 
small  venous  branches  to  the  nerve-fiber  layer,  in  which  they  form 
a  venous  plexus,  side  by  side  with  the  arterial  plexus. 

The  arteries  of  the  retina  are  of  smaller  caliber  than  the  veins. 
The  larger  arteries  possess  a  muscular  layer  ;  the  smaller,  only  an 
adventitia.  All  the  vessels  possess  highly  developed  perivascular 
sheaths.  The  visual-cell  layer  is  nonvascular,  as  are  also  the  fovea 
centralis  and  the  rudimentary  retinal  layers  lying  anterior  to  the 
ora  serrata. 

The  arteries  of  the  retina  anastomose  with  one  another  solely  by 
means  of  capillaries  (end-arteries),  and  it  is  only  in  the  ora  serrata 
that  coarser  venous  anastomoses  exist. 


R  THE  VITREOUS  BODY. 

The  vitreous  body  consists  of  a  semifluid  tissue  containing  very 
few  fixed  cellular  elements  and  only  a  small  number  of  leucocytes. 
The  latter  are  found  only  on  the  surface  of  the  vitreous  humor,  be- 
tween it  and  the  retina.  Thin  structureless  lamellae  and  fibers 
occur  throughout  the  entire  vitreous  body,  with  the  exception  of 
the  hyaloid  canal.  These  are  particularly  numerous  at  the  per- 
iphery and  especially  in  the  region  of  the  ciliary  body.  The  outer  or 
hyaloid  membrane  of  the  vitreous  body,  separating  the  latter  from 
the  retina,  is  somewhat  thicker  in  the  region  of  its  close  attachment 
around  the  physiologic  excavation  of  the  optic  nerve  and  to  the  ex- 
ternal limiting  membrane  of  the  retina  in  the  ciliary  region.  In  the 
latter  region  the  hyaloid  membrane  is  closely  connected  with  the 
epithelium  of  the  pars  ciliaris  retinae.  It  does  not,  however,  pene- 
trate into  and  between  the  ciliary  processes,  but  extends  like  a 
bridge  over  the  furrows  between  them.  This  arrangement  gives 
rise  to  spaces,  the  recessus  camera  posteriori*,  which  form  a  division 
of  the  posterior  chamber,  and  are  inclosed  between  the  hyaloid 
membrane,  the  ciliary  processes,  the  suspensory  ligament  of  the  lens, 
and  the  lens  itself;  these  spaces  are  filled  with  aqueous  humor. 
In  the  region  of  the  ciliary  processes  the  hyaloid  membrane  splits 
up  into  numerous  fibers,  which  diverge  fan-like  toward  the  lens  and 
become  blended  with  the  outer  lamella  of  the  lens-capsule.  Those 
coming  from  the  free  ends  of  the  ciliary  processes  become  attached 


428  THE    EYE. 

along  the  equator  of  the  lens  and  to  the  adjacent  posterior  portion 
of  the  lens-capsule.  On  the  other  hand,  the  fibers  originating  be- 
tween the  ciliary  processes  attach  themselves  to  the  anterior  sur- 
face of  the  lens-capsule  in  the  immediate  vicinity  of  the  equator. 
Together  these  fibers  constitute  the  zomda  ciliaris,  zonule  of  Zinn,  or 
the  suspensory  ligament  of  the  lens.  Between  these  fibers  of  the 
zonula  and  the  lens  itself  there  is,  consequently,  a  circular  canal 
divided  by  septa,  the  canal  of  Petit,  which  communicates  by  open- 
ings with  the  anterior  chamber. 


G.  THE  CRYSTALLINE  LENS. 

As  we  have  already  seen,  the  crystalline  lens  originates  as  an 
ectodermic  invagination,  which  then  frees  itself  from  the  remaining 
ectoderm  in  the  shape  of  a  vesicle  and  becomes  transformed  into 
the  finished  lens.  In  this  process  the  cells  of  the  inner  wall  of  the 
vesicle  become  the  lens-fibers,  while  those  of  the  outer  portion  re- 
main as  the  anterior  epithelium  of  the  lens.  The  lens  is  surrounded 
on  all  sides  by  the  lens-capsule. 

The  lens  capsule  is  a  homogeneous  membrane,  nearly  twice  as 
thick  on  the  anterior  surface  of  the  lens  as  on  the  posterior.  Its 
chemic  reactions  differ  from  those  of  connective  tissue,  and  in  this 
respect  it  may  be  compared  with  the  membranae  propriae  of 
glands.  In  sections  the  lens  capsule  appears  to  possess  a  tangen- 
tial striation  ;  under  the  influence  of  certain  reagents,  and  under 
proper  preliminary  treatment,  lamellae  may  be  detached  from  its 
surface  which  are  found  to  be  directly  connected  with  the  fibers 
of  the  suspensory  ligament. 

The  anterior  epithelium  consists,  in  the  fetus,  of  columnar  cells  ; 
in  children,  of  cells  approaching  the  cubic  type  ;  and  in  the  adult,  of 
decidedly  flattened  cells.  Toward  the  equator  of  the  lens,  in  the 
so-called  transitional  zone,  the  cells  increase  in  height  and  gradually 
pass  over  into  the  lens  fibers. 

The  lens  fibers  are  also  derivatives  of  epithelial  cells  ;  they  are 
long,  flattened,  hexagonal  prisms,  which  extend  through  the  entire 
thickness  of  the  lens.  In  the  adult  the  lens  may  be  differentiated 
into  a  resistant  peripheral  and  a  softer  axial  substance.  The  sur- 
faces of  the  fibers  present  irregularities,  and  it  is  with  the  help  of 
these  serrations  and  a  cement  substance  that  the  fibers  are  bound 
together.  Each  fiber  possesses  one  or  more  nuclei,  which,  although 
they  have  no  constant  position,  are  usually  found  in  the  middle  of 
the  fibers  situated  near  the  lens-axis,  and  in  the  anterior  third  of 
those  at  some  distance  from  the  axis.  The  course  of  the  fibers  in 
the  lens  is  extremely  complicated. 


INTERCHANGE    OF    FLUIDS    IN    THE    EYEBALL.  429 


H.  THE  FETAL  BLOOD-VESSELS  OF  THE  EYE. 

In  the  eye  of  the  embryo  the  vitreous  body  and  the  capsule  of 
the  lens  contain  blood-vessels.  The  vessel  which  later  becomes 
the  central  artery  of  the  retina  passes  through  the  space  sub- 
sequently occupied  by  the  vitreous  body  as  far  as  the  posterior  sur- 
face of  the  lens  (anterior  hyaloid  artery)  and  branches  in  the  region 
of  the  posterior  and  anterior  lens-capsule.  The  anterior  vascular 
membrane  of  the  lens  capsule  of  the  embryo  is  known  as  the 
incinbrana  capsulopupillaris ,  and  that  portion  corresponding  to  the 
pupil,  as  the  membrana  pupillaris.  In  the  embryo  numerous  other 
vessels  arise  at  the  papilla  and  extend  over  the  surface  of  the 
vitreous  body  close  to  the  hyaloid  membrane  ;  these  are  the  pos- 
terior hyaloid  arteries.  These  vessels  later  disappear.  In  place  of 
the  anterior  hyaloid  artery  there  remains  in  the  vitreous  humor  a 
transparent  cylindric  cord  containing  no  fibers  nor  lamellae,  as  is  the 
case  in  the  remaining  portion  of  the  vitreous  body,  and  consisting 
of  a  more  fluid  substance  ;  this  is  the  hyaloid  canal,  or  the  canal  of 
Clog  net. 

With  regard  to  the  posterior  hyaloid  vessels,  the  generally  ac- 
cepted theory  is  that  they  later  enter  into  the  formation  of  the 
retinal  vessels.  Little  is  known  as  to  the  details  of  this  process  ; 
but  the  fact  remains  that,  in  the  rabbit,  for  instance,  the  larger 
branches  of  the  retinal  vessels  are  internal  to  the  inner  limiting 
membrane,  and,  therefore,  within  the  vitreous  body,  and  that  they 
send  smaller  branches  into  the  retina  (His,  80). 


L  INTERCHANGE  OF  FLUIDS  IN  THE  EYEBALL. 

The  anterior  lymph-channels  of  the  eye  comprise  (i)  the 
lymph-canaliculi  of  the  cornea,  which  communicate  with  similar 
structures  in  the  sclera ;  (2)  the  system  of  the  anterior  chamber, 
which  is  indirectly  connected,  on  the  one  hand,  with  the  canal  of 
Schlemm  by  means  of  the  spaces  of  Fontana,  and  with  the  stroma 
iridis,  into  which  the  ligamentum  pectinatum  extends  ;  while,  on  the 
other  hand,  it  communicates  with  the  posterior  chamber  and  its 
recesses,  and  with  the  canal  of  Petit. 

In  the  posterior  region  of  the  eyeball  are  the  lymph-channels 
of  the  retina  (the  perivascular  spaces),  those  of  the  optic  nerve,  the 
space  between  the  pigment  layer  and  the  remaining  portion  of  the 
retina  (interlaminar  space,  Rauber),  and  the  lymph-spaces  of  the 
choroid  and  sclera.  The  influx  and  efflux  of  intraocular  fluid 
occur  principally  by  means  of  filtration.  The  influx  takes  place 
through  the  ciliary  processes  ;  that  the  choroid  has  to  do  with  this 
process  is  very  improbable.  The  efflux  takes  place  through  the 
veins  of  the  canal  of  Schlemm,  into  which  the  fluid  filters  through 
the  cement  lines  of  the  endothelial  lining  of  the  canal  of  Schlemm, 


43O  THE    EYE. 

finally  emptying  into  the  anterior  ciliary  veins.  A  posterior  efflux 
from  the  vitreous  body  probably  does  not  exist,  or  at  least  occurs 
to  a  very  limited  extent.  The  anterior  chamber  possesses  no  efferent 
lymph-vessels  (Leber,  95). 


JL  THE  PROTECTIVE  ORGANS  OF  THE  EYR 

J.  THE  LIDS  AND  THE  CONJUNCTIVA. 

At  the  end  of  the  second  month  of  embryonic  life  the  eyelids 
begin  to  develop  in  the  shape  of  two  folds  of  skin.  At  the  end 
of  the  third  month  these  folds  come  in  contact  in  the  region  of 
what  is  later  the  palpebral  fissure,  and  grow  together  at  their  outer 
epithelial  margins.  Shortly  before  birth  the  two  lids  again  separate 
and  the  definitive  palpebral  fissure  is  formed. 

The  eyelids  show  three  distinct  layers  :  (i)  the  external  cutis, 
which  presents  special  structures  at  its  free  margin  and  continues 
about  I  mm.  inward  from  the  inner  border  of  the  free  margin  ;  (2) 
the  mucous  membrane,  or  palpebral  conjunctiva,  beginning  from 
this  line  and  covering  the  entire  internal  surface  ;  and  (3)  a  middle 
layer. 

1.  The  cuticular  portion  of  the  eyelid  consists  of  a  thin  epider- 
mis and  a  dermis  poorly  supplied  with  papillae.   Fine  lanugo-like  hairs 
with  small  sebaceous  glands  and  a  few  sweat-glands  are  distributed 
over  its  entire  surface.     The  cutaneous  connective   tissue  is  very 
loose,  contains  very  few  elastic  fibers,  and  is  supplied  with  pigment 
cells  in  the  superficial  layers.     At  the  lid-margin  the  papillae  are 
well   developed  and  the  epidermis  is  somewhat  thickened.     The 
anterior  margin  supports  several  rows  of  larger  hairs,  the  cilia,  the 
posterior  row  of  which  possesses,  besides  the  sebaceous  glands, 
modified  sweat-glands,  the  ciliary  glands  of  Moll,  which  also  empty 
into  the  hair  follicles.    The  eyelids  are  further  provided  with  numer- 
ous glands,  known  as  the   Meibomian   or  tarsal   glands.      About 
thirty  of  these  glands  are  found  in  the  upper,  a  slightly  smaller 
number  in  the  lower,  lids.     They  lie  within  the  tissue  of  the  tarsus 
vertical  to  the  palpebral  margin.      Each  gland  consists  of  a  tubular 
duct,  lined  by  stratified  squamous  epithelium,  beset  with  numerous 
simple  or  branched  alveoli  lined  by  a  stratified,  cubic  epithelium  in 
every  respect  similar  to  that  lining  the  alveoli  of  sebaceous  glands. 
The  ducts  of  these  glands  terminate  at  the  palpebral  margin  poste- 
rior to  the  cilia. 

2.  The  conjunctival  portion  of  the  eyelids  is  lined  by  a  simple 
pseudostratified  columnar  epithelium,  possessing  two  strata  of  nuclei. 
This  is  continuous  with  the  bulbar  conjunctiva  at  the  conjunctival 
fornix,  and  is  characterized  by  the  occasional  presence  of  folds  and 
sulci.      Longitudinal   folds   in   the  upper  portion   of  the   upper  lid 
running  parallel  with  the  lid-margin  are  frequently  present.    Goblet 
cells  are  usually  found  in  the  epithelium.     According  to  W.  Pfitz- 


THE  PROTECTIVE  ORGANS  OF  THE  EYE. 


431 


ner  (97),  the  epithelium  of  the  conjunctiva  consists  of  two  or  three 
strata  of  cells,  of  which  the  more  superficial  possess  a  cuticular 
margin.  Certain  structures  which  have  always  been  regarded  as 
goblet  cells  are  in  all  probability  similar  to  the  cells  of  Ley  dig — i.  e., 
mucous  cells,  which  do  not  pour  their  secretion  out  over  the  sur- 
face of  the  epithelium.  Some  lymphoid  tissue  is  always  found  in 
the  stratum  proprium  of  the  mucous  membrane,  and  occasionally  it 


Subcutis. 


Hair  and  sebace-    — 
ous  gland.  V 


Musculus  or-  -T- 
bicularis.         \ 


Conjunctiva. 


Loose  connective 
tissue. 


Meibomian 
glands. 


Cilium. 


Fig.  341. — Cross-section  of  upper  eyelid  of  man  ;  the  blood-vessels  injected.  By 
reason  of  the  characteristic  arrangement  of  the  capillaries  in  the  several  layers  of  tissue, 
the  extent  and  arrangement  of  these  may  be  readily  ascertained. 


is  seen  to  form  true  lymph-nodules.  It  is  of  some  interest  to  note 
that  a  marked  production  of  these  lymph-nodules  occurs  in  certain 
diseases.  Such  lymph-nodules  are  usually  associated  with  epithe- 
lial crypts,  which  fact  led  Henle  to  regard  them  as  glandular  forma- 
tions. Small  glands  with  a  structure  similar  to  that  of  the  lacrimal 
glands  are  also  present  in  the  palpebral  conjunctiva  ;  they  are  found 


432  THE    EYE. 

in  the  upper  eyelid,  at  the  outer  angle  of  the  conjunctival  fornix. 
Similar  glands  occur  also  at  the  mesial  angle  of  the  fornix. 

3.  Besides  the  tarsus  (fibrocartilage)  the  middle  layer  of  the  eye- 
lid contains  :  (i)  The  musculus  orbicularis  oculi,  which  lies  beneath 
the  subcutaneous  tissue.  At  the  margin  of  the  lid  this  structure 
gives  off  the  musculus  ciliaris  Riolani,  which  is  composed  of  two 
fasciculi  separated  by  the  tarsus.  (2)  The  connective  tissue  be- 
tween the  bundles  of  the  musculus  orbicularis  oculi.  (3)  The  con- 
nective tissue  lying  behind  the  latter  and  the  tarsus.  In  the  upper 
lid  the  connective  tissue  mentioned  under  2  and  3  is  connected  with 
the  tendon  of  the  musculus  palpebralis  superior.  The  latter  is 
composed  of  smooth  muscle-fibers,  and  is  regarded  as  a  continua- 
tion of  the  middle  portion  of  the  striated,  voluntary  musculus  leva- 
tor  palpebrae  superioris.  The  middle  layer  of  the  lower  lid  is  struc- 
turally analogous,  except  that  here  the  inferior  rectus  muscle  takes 
the  place  of  the  levator  palpebrae. 

The  blood-vessels  of  the  eyelid  lie  directly  in  front  of  the  tarsus, 
and  from  this  region  supply  adjacent  parts  ;  they  reach  the  poste- 
rior portion  of  the  lid  either  by  penetrating  the  tarsus  or  by  encir- 
cling it  (Waldeyer,  74). 

The  "  third  eyelid,"  the  plica  semilunaris,  contains,  when  well 
developed,  a  small  plate  of  hyaline  cartilage. 

At  the  fornix  the  epithelium  of  the  palpebral  conjunctiva  be- 
comes continuous  with  the  two-  or  three-layered  squamous  epithe- 
lium of  the  conjunctiva  bulbi.  Beneath  this  epithelium  is  found  a 
loose  fibre-elastic  connective  tissue,  presenting  subepithelial  papillae, 
and  quite  vascular.  In  it  are  found  medullated  nerve-fibers,  some 
of  which  terminate  in  free  sensory  nerve-endings  in  the  conjunctival 
epithelium  ;  others  terminate,  especially  near  the  corneal  margin,  in 
end-bulbs  of  Krause  ;  and  still  others  may  be  traced  to  the  cornea, 
to  terminate  in  a  manner  previously  described. 

2.  THE  LACRIMAL  APPARATUS. 

The  lacrimal  apparatus  consists  of  the  lacrimal  glands,  their  ex- 
cretory ducts,  the  lacrimal  puncta  and  canaliculi,  the  lacrimal  sac, 
and  the  nasal  duct. 

The  lacrimal  gland  is  separated  into  two  portions,  of  which 
the  one  lies  laterally  against  the  orbit  and  the  other  close  to  the 
upper  lateral  portion  of  the  superior  conjunctival  fornix.  The 
structure  of  the  gland  is,  on  the  whole,  that  of  a  serous  gland 
(parotid),  with  the  difference  that  the  intralobular  ducts  are  not 
lined  by  a  striated  epithelium  such  as  is  found  in  the  salivary 
tubules,  and  that  those  cells  which  are  wedged  in  between  the 
secretory  elements  and  functionate  as  sustentacular  cells  (basket- 
cells)  are  here  much  more  highly  developed. 

The  excretory  ducts  of  the  orbital  division  generally  pass  by  the 
conjunctival  half  of  the  gland,  taking  up  a  few  ducts  from  the  latter 


TECHNIC.  433 

as  they  go,  and  finally  empty  on  the  surface  of  the  conjunctiva. 
Aside  from  these,  the  lateral  portion  of  the  gland  possesses  also 
independent  ducts.  All  the  excretory  ducts  are  lined  by  columnar 
epithelium  and  surrounded  by  a  relatively  thick  connective-tissue 
wall  having  inner  longitudinal  and  outer  circular  fibers.  From  the 
lateral  portion  of  the  conjunctival  culdesac,  into  which  the  secre- 
tion is  brought  by  the  excretory  ducts  of  the  lacrimal  gland,  the 
secretion  passes  into  the  capillary  space  of  the  sac,  and  is  then 
evenly  distributed  by  means  of  the  sulci  and  papillae  over  the  con- 
junctival surface  of  the  lid.  In  this  manner  the  secretion  reaches 
the  mesial  angle  of  the  lid,  whence  it  passes  through  the  lacrimal 
puncta  into  the  lacrimal  canals. 

The  nerve  supply  of  the  lacrimal  glands  is  from  the  sym- 
pathetic nervous  system.  The  neuraxes  of  sympathetic  neurones 
accompany  the  gland  ducts  and  form  plexuses  about  the  alveoli, 
the  terminal  branches  of  which  may  be  traced  to  the  gland  cells. 

The  lacrimal  canals  are  lined  by  stratified  squamous  epi- 
thelium, and  possess  a  basement  membrane  as  well  as  a  con- 
nective-tissue layer  containing  circularly  disposed  elastic  elements. 
Externally  we  find  a  layer  of  transversely  striated  muscle-fibers. 

The  lacrimal  sac  is  provided  with  a  simple  pseudostratified 
columnar  epithelium  having  two  strata  of  nuclei.  In  it  goblet  cells 
are  also  found.  The  nasal  duct  is  lined  by  a  similar  epithelium. 
The  connective-tissue  wall  of  the  latter  and  that  of  the  lacrimal 
sac  come  in  contact  with  the  periosteum  ;  between  them  is  a  well- 
developed  vascular  plexus.  Stratified  squamous  and  ciliated  epi- 
thelium have  been  described  as  being  present  in  the  nasal  duct,  as 
well  as  mucous  glands  in  both  nasal  duct  and  lacrimal  sac.  (See 
works  of  M.  Schultze,  72  ;  Schwalbe,  87.) 


TECHNIC 

316.  The  eyes  of  the  larger  animals,  after  having  been  previously 
cleaned  by  removing  the  muscles  and  loose  connective  tissue,  are  placed 
in   the  fixing  fluid  and  cut  into  two  equal  parts  by  means  of  an  equa- 
torial incision.     Smaller  eyes  with  thin  walls  may  be  fixed  whole. 

Miiller's  fluid  (T.  27),  nitric  acid  (T.  25),  and  Flemming's  fluid 
(T.  17)  are  usually  employed  as  fixing  agents.  After  fixing  in  one  of 
these  fluids,  different  parts  of  the  eyeball  are  imbedded  in  celloidin  or  cel- 
loidin -paraffin  and  then  sectioned. 

317.  The  corneal  epithelium  is  best  macerated  in  33%  alcohol ;  the 
membrane  of  Descemet  may  be  impregnated  with  silver.     In  order  to 
bring  the  fibers  of  the  latter  into  view,  Nuel  recommends  an  injection  of 
i%  to  2f-/f  formic  acid  into  the  anterior  chamber  of  the  eye  of  a  dove  or 
a  rabbit,  after  having  drawn  off  the  aqueous  humor.     The  cornea  is  then 
cut  out,  and  fixed  for  from  three  to  five  minutes  in  osmic  acid. 

318.  The  substantia  propria  is  examined  either  by  means  of  sections 
or  by  means  of  teased  preparations  from  a  cornea  macerated  in  lime- 
water  or  potassium  permanganate.     The  sections  are  stained  with  picro- 

28 


434  THE  EYE- 

carmin  (Ranvier).  The  corneal  spaces  and  canaliculi  may  be  demon- 
strated in  two  ways  with  the  aid  of  silver  nitrate ;  either  the  fresh  cornea 
of  a  small  animal  is  stripped  of  its  epithelium,  cauterized  with  a  solid 
stick  of  silver  nitrate,  and  then  examined  in  water,  in  which  case  the 
corneal  spaces  and  their  canaliculi  show  light  upon  a  dark  ground  (neg- 
ative impregnation)  ;  or  the  corneae  of  larger  animals  are  treated  in  the 
same  manner,  after  which  tangential  sections  are  made  with  a  razor,  and 
placed  in  water  for  a  few  days  ;  in  this  case  the  corneal  spaces  and  their 
canaliculi  show  dark  upon  a  light  ground  (positive  impregnation,  Ran- 
vier, 89). 

319.  By  means  of  Altmann's  oil  method  (T.  112)  casts  of  the  corneal 
spaces  and  their  canaliculi  may  be  made.     Treatment  by  the  gold  method 
often  brings  out  not  only  the  nerves,  but  also  the  corneal  corpuscles  and 
their  processes. 

320.  Ranvier   (89)   especially    recommends  a   ic/c    solution    of   the 
double  chlorid  of  gold  and  potassium  for  the  corneal  nerves.     The  cor- 
nea of  the  frog  is  treated  for  five  minutes  with  lemon-juice,  then  for  a 
quarter  of  an  hour  with  i  %  potassium -gold  chlorid  solution,  and,  finally, 
for  one  or  two  days  with  water  weakly  acidulated  with  acetic  acid  (2 
drops  to  30  c.c.  of  water),  the  whole  process  taking  place  in  the  light. 
Golgi's  method  may  also  be  used,  but  the  gold  method  is  more  certain. 

321.  The  sclera  is  treated  in  a  similar  manner. 

322.  The  pigmentation  of  the  vascular  layer  interferes  with  examina- 
tion, and  albinotic  animals  should  therefore  be  selected  ;  or  the  pigment 
may  be  removed  from  the  previously  fixed  eyeball  with  hydrogen  peroxid 
or  nascent  chlorin.    The  latter  method  is  applied  exactly  as  in  cases  where 
the  removal  of  osmic  acid  is  desired  (T.  144). 

323.  The  adult  lens  is  sectioned  with  difficulty,  as  it  becomes  very 
hard  in  all  .fixing  fluids.    The  anterior  capsule  of  the  lens  may  be  removed 
from  previously  fixed  specimens  and  examined  by  itself.      The  lens-fibers 
are  demonstrated  by  maceration  in  y$  alcohol  (twenty-four  hours)  or  in 
strong  nitric  acid.     Before  immersion  the  lens-capsule  is  opened  by  a 
puncture. 

324.  The  retina  can  rarely  be  kept  unwrinkled  in  eyes  that  have  been 
fixed  whole.       The  eyeball  should  therefore  be  opened  in  the  fixing  fluid 
and  the  latter  permitted  to  act  internally ;  or  the  external  tunics  are 
removed,  thereby  enabling  the  fixing  fluid  to  act  externally. 

325.  Ranvier   recommends   subjecting  the  eyes  of  smaller  animals 
(mouse,  triton)  for  a  quarter  or  half  hour  to  the  action  of  osmic  acid 
fumes  (vid.  T.  16),  after  which  the  eyes  are  opened  in  ^  alcohol  with 
the  scissors.     At  the  end  of  three  or  four  hours  the  posterior  half  of  the 
eye  is  stained  for  some  time  in  picrocarmin  (T.  67),  then  carried  over 
into  i%  osmic  acid  for  twelve  hours,  washed  with  water,  treated  with 
alcohol,  and  cut. 

In  osmic  acid  preparations  the  rod-nuclei  show  dark  transverse  bands, 
a  condition  due  to  the  fact  that  the  end-regions  of  the  nuclei  stain  more 
deeply. 

The  retina  is  a  good  object  for  differential  staining,  as,  for  instance, 
with  hematoxylin-eosin,  hematoxylin -orange  G,  etc.  The  latter  combina- 
tion is  particularly  successful  in  staining  the  rod-  and  cone-ellipsoids. 
The  examination  of  tangential  sections  should  not  be  omitted. 


THE    EXTERNAL    EAR.  435 

326.  With  the  retina  the  best  results  are  obtained  by  means  of  Golgi's 
method.     Attention  must  be  called  to  the  fact  that  the  supporting  struc- 
tures of  the  retina  are  more  easily  impregnated  than  the  nervous  elements, 
and  that  the  latter  can  be  demonstrated  to  any  extent  only  in  very  young 
eyes. 

327.  Ramon  y  Cajal  (94)  recommends  the  following  method,  modi- 
fied after  Golgi :   After  the  removal  of  the  vitreous  humor  the  posterior 
half  of  the  eyeball  is  placed  for  one  or  two  days  in  a  mixture  containing 
3%  potassium  bichromate  20  c.c.  and  ic/c  osmic  acid  5  or  6  c.c.     The 
pieces  are  then  dried  with  tissue  paper  and  placed  in  a  0.75%  silver 
nitrate  solution  for  an  equal  length  of  time.     Without  washing,  the  pieces 
are  immersed  for  from  twenty-four  to  thirty-six  hours  in  a  mixture  con- 
taining 3^  potassium  bichromate  20  c.c.,  and  i%  osmicacid  2  or  3  c.c., 
and  then  again  carried  over   into  a    0.75%   silver  nitrate   solution  for 
twenty-four  hours.      In  order  to  prevent  precipitation  it  is  advisable  to 
roll  up  the  retina  before  treating,  and  to  cover  it  with  a  thin  layer  of  a 
thin  celloidin  solution,  which  prevents  it  from  again  unrolling. 

328.  The  methylene-blue  method  (T.  312)  will  also  bring  out  the 
nervous  elements  of  the  retina,  although  the  results  are  not  quite  so  satis- 
factory as  those  obtained  by  Golgi's  method. 


IX.  THE  ORGAN  OF  HEARING. 

THE  ear,  the  organ  of  hearing,  consists  of  three  parts  :  (i)  The 
external  ear,  including  the  pinna  or  auricle  and  the  external  audi- 
tory canal ;  (2)  the  middle  ear,  tympanum,  or  tympanic  cavity, 
containing  the  small  ear  bones  and  separated  from  the  external 
auditory  canal  by  the  tympanic  membrane,  but  communicating  with 
the  pharynx  by  means  of  the  Eustachian  tube ;  (3)  the  inner  ear, 
or  labyrinth,  consisting  of  a  bony  and  a  membranous  portion,  the 
latter  lined  by  epithelial  cells,  especially  differentiated  in  certain 
regions  to  form  a  neuro-epithelium,  in  which  the  auditory  nerves 
terminate.  The  first  two  parts  serve  for  the  collection  and  trans- 
mission of  the  sound-waves  ;  the  complicated  labyrinth,  with  its 
differentiated  neuro-epithelium,  for  the  perception  of  the  same. 
Figure  342  presents  in  a  schematic  way  the  relationships  of  the 
parts  here  mentioned. 


A.  THE  EXTERNAL  EAR. 

The  cartilage  of  the  ear,  including  that  of  the  external  auditory 
passage,  is  of  the  elastic  variety,  but  differs  from  typical  elastic  carti- 
lage in  that  it  contains  areas  entirely  free  from  elastic  fibers.  The 
elastic  reticulum  is,  however,  never  absent  near  the  perichondrium. 
The  skin  covering  the  pinna  is  thin,  and  in  it  are  found  hairs  with 
relatively  large  sebaceous  glands  ;  sweat-glands  are  found  on  the 
outer  surface. 


436 


THE    ORGAN    OF    HEARING. 


The  skin  lining  the  cartilaginous  portion  of  the  external  auditory 
canal  possesses  very  few  pronounced  papillae,  and  is  characterized 
by  the  presence  of  so-called  ceruminous  glands,  which  represent 
modified  and  very  highly  differentiated  sweat-glands.  Two  or  three 
of  the  latter  sometimes  become  confluent,  and  then  possess  only  a 
single  excretory  duct,  which,  as  a  rule,  empties  into  a  hair  follicle 
near  the  surface  of  the  skin.  The  corium  is  somewhat  mobile. 

The  skin  lining  the  osseous  portion  of  the  external  auditory 
canal  is  supplied  with  neither  hair  nor  glands,  and  possesses  slender 
papillae,  especially  in  the  neighborhood  of  the  tympanic  membrane. 
The  corium  is  closely  attached  to  the  periosteum. 

The  tympanic  membrane  consists  of  a  tense  and  a  flaccid  portion. 


Pinna 


Acoustic 

nerve. 

—  Ductusendo- 
lymphaticus 
Saccus  endo- 
lymphaticus 
Temporal 

bone. 


h  c  £  «  W  >• 

Fig.  342. — Schematic  representation  of  the  complete  auditory  apparatus  (Schwalbe) 


It  forms  a  part  of  both  the  external  and  the  middle  ear.  From 
without  inward,  the  following  layers  may  be  differentiated  :  (i)  the 
cutaneous  layer ;  (2)  the  lamina  propria ;  and  (3)  the  mucous  layer. 

The  epidermis  of  the  cutaneous  layer  is  identical  in  structure 
with  that  of  the  outer  skin,  except  that  the  superficial  layers  of  the 
stratum  corneum  contain  nucleated  cells.  The  corium  is  very  thin, 
except  along  the  course  of  the  manubrium  of  the  malleus,  where  it 
is  thickened,  forming  the  so-called  cuticular  ridge,  which  possesses 
papillae  and  is  supplied  with  vessels  and  nerves. 

The  lamina  propria  ends  peripherally  in  a  thickened  ring  of  fibro- 
cartilaginous  tissue,  the  annulus  fibrosus,  which  unites  at  the  sulcus 


THE    MIDDLE    EAR.  437 

tympanicus  with  the  periosteum  of  the  latter.  The  lamina  propria 
is  composed  of  connective-tissue  fibers,  in  which  two  layers  may  be 
distinguished — externally,  the  radiate  fibers,  the  stratum  radiatum, 
and  internally,  the  circular  fibers,  the  stratum  circular e.  The  ex- 
ternal radiate  layer  extends  from  the  annulus  to  the  umbo  and 
manubrium,  and  is  interrupted  in  the  flaccid  portion  of  the  tympanic 
membrane  by  the  upper  fourth  of  the  manubrium  and  the  short 
process  of  the  malleus  ;  it  gradually  thins  out  toward  the  center 
until  it  finally  disappears  in  the  vicinity  of  the  umbo.  The  fibers 
of  the  inner  (circular)  layer  are  circularly  disposed.  This  layer  is 
thickest  at  the  periphery  of  the  tympanic  membrane,  becoming 
gradually  thinner  toward  the  lower  end  of  the  manubrium,  where 
it  disappears.  Between  the  two  layers  of  the  lamina  propria  is  a 
small  quantity  of  loose  connective  tissue.  The  manubrium  of  the 
malleus  is  inclosed  within  the  tympanic  membrane.  This  is  due  to 
the  union  of  the  fibers  of  the  radial  layer  with  the  outer  strata  of 
the  manubrial  perichondrium,  the  handle  of  the  malleus  being  here 
covered  by  a  thin  layer  of  cartilage.  In  the  posterior  upper  quad- 
rant of  the  tympanic  membrane  the  two  layers  of  the  lamina  propria 
intermingle,  forming  irregularly  disposed  bundles  and  trabeculae, 
the  dendritic  fibrous  structures  of  Gruber. 

The  mucous  layer  of  the  tympanic  membrane  consists  of  sim- 
ple squamous  epithelium  separated  from  the  lamina  propria  by  a 
thin  connective-tissue  layer  containing  but  few  cells.  It  likewise 
extends  over  the  handle  of  the  malleus.  In  the  flaccid  portion  of 
the  tympanic  membrane  the  lamina  propria  disappears,  so  that  in 
this  region  the  cutaneous  layer  and  the  mucous  membrane  are  in 
direct  contact. 


B.  THE  MIDDLE  EAR. 

The  middle  ear,  or  tympanum,  is  a  small  irregular  cavity,  filled 
with  air,  situated  in  the  petrous  portion  of  the  temporal  bone  be- 
tween the  bony  wall  of  the  inner  ear  and  the  tympanic  membrane, 
and  communicates  with  the  pharynx  through  the  Eustachian  tube. 
It  contains  the  small  bones  of  the  ear,  their  ligamentous  attach- 
ments, and,  in  part,  the  muscular  apparatus  moving  them. 

The  mucous  membrane  lining  the  tympanic  cavity  is  folded  over 
the  ossicles  and  ligaments  of  the  tympanum  and  is  joined  to  that  of  the 
tympanic  membrane  and  the  Eustachian  tube,  the  line  of  junction 
with  the  former  being  marked  by  the  presence  of  papilla-like  eleva- 
tions. 

The  epithelium  of  this  mucous  membrane  is  a  simple  pseudo- 
stratified  ciliated  epithelium,  having  two  strata  of  nuclei.  Cilia  are, 
however,  lacking  on  the  surface  of  the  auditory  ossicles,  on  their 
ligaments,  and  on  the  promontory  of  the  inner  wall,  as  well  as  on  the 
tympanic  membrane.  The  mucosa  of  the  mucous  membrane  is  in- 
timately connected  with  the  periosteum,  and  contains  short  isolated 


438 


THE    ORGAN    OF    HEARING. 


alveolar  glands,  especially  in  the  neighborhood  of  the  opening  of 
the  Eustachian  tube. 

The  "auditory  ossicles"  are  true  bones  with  Haversian  canals 
and  lamellae  ;  with  the  exception  of  the  stapes,  they  contain  no 
marrow-cavity.  Very  distinct  perivascular  spaces  are  seen  sur- 
rounding the  vessels  in  the  canals  (Rauber).  The  malleus  articu- 
lates with  the  incus,  both  articular  surfaces  being  covered  with 
hyaline  cartilage.  Within  this  articulation  we  find  a  fibrocartilagin- 
ous  meniscus,  and  at  the  summit  of  the  short  limb  of  the  incus 
another  small  cartilage  plate.  Between  the  lenticular  process  of  the 
incus  and  the  capitulum  of  the  stapes  is  another  articulation,  also 
provided  with  cartilaginous  articular  surfaces.  The  basal  plate  of 


Portion  of  Eusta- 
chian tube  free 
from  glands. 


Cartilage. 


Mucosa  of  the 
pharynx. 


Glands. 


Glands.  -?=--- ~~~ 


Fig.  343. — Cross- section  of  the  Eustachian  tube  with  its  surrounding  parts  ;   X  I2  (from 
a  preparation  by  Professor  Rtidinger). 


the  stapes  is  covered  both  below  and  at  its  edges  with  cartilage,  as 
are  also  the  margins  of  the  fenestra  ovalis  (fenestra  vestibuli).  The 
basal  plate  is  held  in  place  within  the  fenestra  by  an  articulation, 
provided  with  tense  ligamentous  structures  on  the  tympanic  and 
vestibular  sides.  Between  these  the  connective  tissue  is  quite  loose. 
All  the  cartilaginous  portions  of  the  auditory  ossicles,  with  the  ex- 
ception of  the  articular  cartilages,  rest  on  the  periosteum  (Rudin- 
ger,  70). 

The  fenestra  rotunda  (fenestra  cochleae)  is  closed  by  the  secon- 
dary or  inner  tympanic  membrane,  a  connective-tissue  membrane 
containing  vessels  and  nerves,  the  outer  wall  of  which  is  covered  by 


THE    INTERNAL    EAR.  439 

ciliated  epithelium,  the  inner  (the  surface  toward  the  scala  tympani) 
by  flattened  endothelial  cells. 

In  the  antrum  and  mastoid  cells,  the  mucosa  of  the  mucous 
membrane  is  immovably  fixed  to  the  periosteum.  The  epithelium 
is  of  the  simple  squamous  variety  and  is  nonciliated. 

The  mucous  membrane  of  the  osseous  portion  of  the  Eustachian 
tube  is  very  thin,  and  its  mucosa  is  intimately  connected  with  the 
periosteum.  Its  epithelium  is  of  the  simple  pseudostratified  ciliated 
variety,  having  two  strata  of  nuclei.  There  are  no  glands.  The 
mucous  membrane  of  the  cartilaginous  portion  of  the  Eustachian 
tube  is  thicker,  and  its  epithelium,  which  is  of  the  stratified  ciliated 
variety,  is  higher,  and  often  contains  goblet-cells.  Lymphoid  tissue 
may  be  demonstrated  in  the  mucosa  of  this  portion,  and  occasion- 
ally structures  resembling  lymph-nodules  are  found,  especially  in  the 
vicinity  of  the  pharyngeal  opening  of  the  tube.  In  the  cartilaginous 
portion  of  the  tube  are  mucous  glands,  which  are  particularly 
numerous  in  the  vicinity  of  the  pharyngeal  opening  (Riidinger, 

72,   2). 

C  THE  INTERNAL  EAR. 

The  internal  ear  consists  of  an  osseous  and  a  membranous  por- 
tion, the  osseous  and  the  membranous  labyrinths ;  the  latter  is  con- 
tained within  the  former,  and,  although  smaller,  presents  the  same 


Superior  semicircular  canal. 


Horizontal  semi- 
circular canal. 
Posterior  semi- 
circular canal. 


Ampulla.  mcrr--   •«*-...         •«,  •  . ^  ,»  n    Bony  cochlea> 


Vestibule.        Fenestra  rotunda. 

Fig.  344. — Right  bony  labyrinth,  viewed  from  outer  side  :  The  figure  represents  the 
appearance  produced  by  removing  the  petrous  portion  of  the  temporal  bone  down  to  the 
denser  layer  immediately  surrounding  the  labyrinth  (from  Quain,  after  Sommering). 

general  shape.    The  two  structures  are  separated  by  a  lymph-space 
containing  the  perilymph. 

In  the  bony  labyrinth  we  recognize  a  central  portion  of  ovoid 
shape,  known  as  the  vestibule,  the  outer  wall  of  which  forms  the 
inner  wall  of  the  tympanum  and  presents  two  openings,  the  fenestra 
ovalis  and  the  fenestra  rotunda,  separated  by  a  ridge  known  as  the 
promontory.  This  ridge  becomes  continuous  with  the  lower  portion 


440 


THE    ORGAN    OF    HEARING. 


of  the  bony  cochlea,  anterior  and  mesial  to  the  vestibule  and  having 
the  shape  of  a  blunt  cone.  From  the  posterior  portion  of  the  ves- 
tibule arise  three  semicircular  canals,  known  respectively  as  the 
external  or  horizontal  semicircular  canal,  the  anterior  superior  vertical, 
and  the  posterior  inferior  vertical  semicircular  canals.  The  canals 
communicate  with  the  vestibule  by  means  of  five  openings,  the 
superior  contiguous  portions  of  the  anterior  and  posterior  canals 
uniting  to  form  the  canalis  communis  before  reaching  the  vestibule. 
The  three  canals  present  near  their  origin  from  the  vestibule  enlarge- 
ments known  as  the  osseous  ampullae.  The  osseous  labyrinth  is 
lined  throughout  by  a  thin  layer  of  periosteum,  covered  by  a  layer 
of  endothelial  cells. 

The  membranous  labyrinth  differs  in  shape  from  the  osseous 


Auditory  nerve 
with  its  vestihu- 
lar  and  cochlear 
branches. 


Ant.  semicircular  canal. 
Ampulla. 


Cochlear  duct. 


Canalis  reuniens.          Ductus         Ampulla, 
endolymphaticus. 


Horizontal  semicir- 
cular canal. 


Fig.  345. — Membranous  labyrinth  of  the  right  ear  from  five-month  human  embryo  (from 
Schwalbe,  after  Retzius). 

labyrinth  in  that,  in  place  of  the  single  chamber  (vestibule)  of  the 
latter,  the  membranous  labyrinth  presents  two  sacs,  the  utriculus 
and  the  sacculus,  united  by  a  narrow  duct,  the  utriculosaccular 
duct.  The  utriculus  is  the  larger,  and  from  it  arise  the  membran- 
ous semicircular  canals.  These  present  ampullae,  situated  within 
the  osseous  ampullae  previously  mentioned.  The  sacculus  com- 
municates with  the  cochlear  duct  by  means  of  the  canalis  reuniens 
(Hensen).  From  the  utriculosaccular  duct  arises  the  ductus 
endolymphaticus,  which  passes  through  the  aqueductus  vestibuli 
and  ends  in  a  subdural  saccus  endolymphaticus  on  the  posterior  sur- 
face of  the  petrous  portion  of  the  temporal  bone. 

In  the  membranous  labyrinth  the  nerves  are  distributed  over 
certain  areas  known  as  the   macula,  cristce,  and  papilla  spiralis. 


THE    INTERNAL    EAR. 


441 


There  is  a  macula  within  the  recess  of  the  utriculus,  the  inacula 
acustica  utriculi  ;  and  another  within  the  sacculus,  the  macula 
aaistica  sacculi  ;  cristae  are  present  in  the  ampullae  of  the  upper, 
posterior,  and  lateral  semicircular  canals,  the  cristce  ampullares  sup., 
post.,  et  lat.  Besides  these,  we  have  the  terminal  arborization  of 
the  acoustic  nerve  in  the  membranous  cochlea,  the  papilla  spiralis 
cochlea,  or  the  organ  of  Corti. 

\.  UTRICULUS  AND  SACCULUS. 

Only  the  inner  wall  of  the  utriculus  is  connected  with  the  peri- 
osteum  of  the  vestibule.     In   this   region  lies  the  corresponding 


Membranous  semicircular  canal. 


Blood-vessel. 


Wall  of  mem- 
branous 
canal. 


- -  ,  „ Epithelium  of  the 

membranous 
canal. 


Ligament  of 
canal. 


Bone. 


Perilymphatic 
spaces. 


Blood-vessel. 

Fig.  346. — Transverse  section  through  an  osseous  and  membranous  semicircular  canal 
of  an  adult  human  being;  X  5°  (after  a  preparation  by  Dr.  Scheibe):  a,  Connective- 
tissue  strand  representing  a  remnant  of  the  embryonic  gelatinous  connective  tissue.  Such 
strands  serve  to  connect  the  membranous  canal  with  the  osseous  wall. 


macula  cribrosa,  through  which  the  nerves  penetrate  to  the  macula 
of  the  utriculus.  The  utriculus  and  sacculus  fill  only  a  part  of  the 
inner  cavity  of  the  osseous  vestibule.  Between  the  osseous  and 
membranous  portions  remains  a  space  traversed  by  anastomosing 
connective -tissue  trabeculae,  and  lined  by  endothelium,  which  also 
forms  an  investing  membrane  around  the  trabeculae.  These  trabe- 
culae pass  on  the  one  side  into  the  periosteum  lining  the  vestibule, 


442  THE    ORGAN    OF    HEARING. 

and  on  the  other,  into  the  wall  of  the  utriculus  and  sacqulus.  The 
cavity  which  they  thus  traverse  represents  a  perilymphatic  space. 
(Compare  Fig.  346,  which  shows  analogous  relations  in  the  semi- 
circular canals.) 

The  wall  of  the  utriculus,  especially  its  inner  portion,  consists 
of  dense  fibrous  connective  tissue,. most  highly  developed  in  the 
region  of  the  .macula  acustica.  In  the  immediate  vicinity  of  the 
macula  utriculi  the  epithelium  of  the  utriculus  is  high  columnar  in 
type  ;  in  the  remaining  portion  it  consists  of  a  single  layer  of  low 
columnar  cells,  with  a  distinct  basement  membrane  ;  the  epithelium 
of  the  macula  itself  is  also  high,  and  is  composed  of  two  kinds  of 
elements — of  sustentacular  elements  and  of  the  so-called  auditory 
hair-cells.  The  sustentacular  cells  are  tall  epithelial  cells  resting 
on  the  basement  membrane  by  means  of  their  single  or  cleft  basal 
plates.  Each  possesses  an  oval  nucleus  lying  at  or  beneath  the 
center  of  the  cell.  The  hair-cells  are  peculiar  cylindric  elements 
with  somewhat  thickened  and  rounded  bases.  One  end  extends  to 
the  surface  of  the  epithelium,  while  the  other,  which  contains  the 
nucleus,  extends  only  to  the  center  of  the  epithelial  layer.  The  free 
end  is  provided  with  a  cuticular  zone  supporting  a  number  of 
long,  stiff  hairs,  which  often  coalesce  to  form  single  threads.  On 
the  surface  of  the  epithelium,  which  must  be  regarded  as  a 
neuro-epithelium,  are  crystals  of  calcium  carbonate,  known  as  oto- 
liths,  each  of  which  incloses  a  minute  central  vacuole  (Schwalbe). 
The  otoliths  are  inclosed  in  a  homogeneous  substance,  the  otolithic 
membrane,  which  coagulates  in  a  network  of  filaments  when  sub- 
jected to  the  action  of  fixing  agents. 

The  nerve-fibers  going  to  -the  macula  penetrate  the  wall,  and, 
under  the  epithelium,  undergo  dichotomous  division,  and,  after  fur- 
ther division,  form,  in  the  region  of  the  basilar  ends  of  the  auditory 
cells,  a  plexus  consisting  of  fine  ramifications,  and  embracing  the 
lower  encts  of  the  auditory  cells.  A  few  fibers  extend  still  further 
upward,  where  their  telodendria  enter  into  intimate  relations  with 
the  acoustic  cells  (v.  Lenhossek,  94,  i). 

The  structure  of  the  sacculus  is  in  every  respect  like  that  of  the 
utriculus,  and  a  further  description  of  it  is  therefore  unnecessary. 


2.  THE  SEMICIRCULAR  CANALS, 

The  membranous  semicircular  canals  are  attached  at  their  con- 
vex surfaces  to  the  periosteum  of  the  .bony  canals,  which  they  only 
partly  fill,  the  remaining  cavity  being  occupied  by  an  eccentrically 
situated  perilymphatic  space  traversed  by  connective-tissue  trabeculae. 
The  walls  of  the  perilymphatic  spaces  of  the  semicircular  canals, 
like  those  surrounding  the  utriculus  and  the  sacculus,  are  lined  by 
endothelium,  which  covers,  on  the  one  hand,  the  periosteal  surface 
of  the  bony  semicircular  canals,  and,  on  the  other  hand,  the  outer 
wall  of  the  membranous  canals,  together  with  the  connective-tissue 


THE    INTERNAL    EAR. 


443 


trabeculae.  The  connective-tissue  walls  of  the  membranous  canals 
are  structurally  similar  to  those  of  the  utricujus  and  sacculus. 
Hensen  compares  their  structure  to  that  of  the  substantia  propria 
of  the  cornea.  In  the  adult,  the  inner  layer  of  the  wall  of  the 
canals  supports  here  and  there  papillary  elevations,  which,  however, 
disappear  along  its  attachment  to  the  bony  semicircular  canal 
(Rudinger,  72/88). 

The  epithelium  lining  the  membranous  semicircular  canals  is 
simple  squamous  in  character  and  very  evenly  distributed  over  the 
entire  inner  surface,  including  the  papillae  previously  mentioned. 
On  the  concave  side  of  each  semicircu- 
lar canal  the  epithelial  cells  are  some- 
what narrower  and  higher.  This  inner 
and  higher  epithelium  (raphe),  extending 
along  the  concave  side  into  the  ampullae, 
marks  the  region  at  which  the  semicir- 
cular canals  were  constricted  off  from 
the  pocket-like  anlagen.  The  epithe- 
lium of  the  ampullae  (Fig.  347),  with 
the  exception  of  that  in  the  region  of  the 
raphe,  is  of  the  squamous  type.  At  the 
cristse  of  the  ampullae,  however,  there  is 
found  a  neuro-epithelium  similar  to  that 
of  the  maculae.  The  cells  adjoining  both 
ends  of  the  cristae  are  high  columnar, 
and  to  these  the  squamous  epithelium 
is  joined.  The  columnar  cells  just  men- 
tioned form  the  so-called  semilunar  fold. 
Otoliths  are  also  present  upon  the  neu- 
ro-epithelium of  the  cristae.  Here  the 
structure  corresponding  to  the  otolithic 
membrane  of  the  utriculus  and  sacculus 
is  called  the  cupula.  In  preserved  spec- 
imens it  presents  the  appearance  of  a 
coagulum,  showing  a  faint  striation  ;  in 

the  fresh  condition,  it  has  never  been  .recognized  as  a  distinct  struc- 
ture, at  least  in  the  lower  classes  of  vertebrates. 


'-  —  d 


Fig.  347. — Part  of  a  verti- 
cal section  through  the  anterior 
ampulla,  showing  the  membran- 
ous wall,  a  portion  of  the  "crista 
acustica,"  and  the  "planum 
semilunatum"  (after  Retzius)  : 
a,  Semilunar  fold  ;  6,  crista  acus- 
tica ;  cy  nerve-fibers ;  d,  blood- 
vessels. 


3.  THE  COCHLEA. 

The  cochlea  consists  of  an  osseous  portion,  the  bony  coclilca, 
a  membranous  portion,  the  cochlear  duct,  and  two  perilymphatic 
canals.  The  bony  cochlea  consists  of  a  central  bony  axis  of  conical 
shape,  the  modiolus,  around  which  is  wound  a  spiral  bony  canal, 
having  in  man  a  little  over  two  and  one-half  turns,  the  modiolus 
forming  the  inner  wall  of  this  canal.  The  summit  of  the  cochlea, 
which  has  the  shape  of  a  blunt  cone,  is  formed  by  the  blind  end  of 
this  bony  canal,  and  is  known  as  the  cupola.  The  modiolus  further 


444  THE    ORGAN    OF    HEARING. 

gives  support  to  a  spiral  plate  of  bone,  the  lamina  spiralis  ossea, 
which  extends  from  the  lower  part  of  the  modiolus,  and,  forming 
two  and  one-half  spiral  turns,  reaches  its  top,  where  it  ends  in  a 
hook-like  process,  the  hamulus.  This  bony  spiral  lamina  partly 
divides  the  bony  cochlear  canal  into  two  parts,  the  division  being 
completed  by  a  fibrous  tissue  membrane,  the  lamina  spiralis  mem- 
branacca,  which  extends  from  the  free  edge  of  the  osseous  spiral 
lamina  to  a  thickened  periosteal  ridge,  the  ligamentum  spirale,  lining 
the  outer  wall  of  the  bony  cochlear  canal.  The  canal  above  the 
lamina  spiralis  (bony  and  membranous)  is  known  as  the  scala 
vestibuli,  that  below  as  the  scala  tympani.  Both  are  perilymphatic 
canals,  and  communicate  in  the  region  of  the  last  half-turn  of  the 
cochlea,  by  means  of  a  narrow  canal,  the  helicotrema,  partly  sur- 
rounded by  the  termination  of  the  bony  spiral  lamina,  the  hamulus. 
The  scala  vestibuli  is  in  free  communication  with  the  perilymphatic 
space  of  the  vestibule  ;  while  the  scala  tympani  communicates  with 
perivascular  spaces  surrounding  the  veins  of  the  cochlear  aqueduct, 
which  latter  empty  into  the  jugular  veins.  The  scala  tympani  ter- 
minates at  the  secondary  tympanic  membrane,  closing  the  fenestra 
rotunda. 

The  cochlear  duct,  which,  as  will  be  remembered,  communicates 
with  the  sacculus  by  means  of  the  canalis  reuniens,  is  a  long  tube 
closed  at  both  ends,  the  one  end  representing  the  vestibular  sac,  or 
ccecnm  vestibulare,  and  the  other  the  cupolar  extremity,  or  cacum 
cupolare,  also  known  as  the  lagena.  The  cochlear  duct  forms  about 
two  and  three-fourths  spiral  turns,  its  length  being  about  3.5  mm. 
Its  diameter  gradually  increases  from  its  lower  to  its  upper  or  distal 
extremity.  The  cochlear  duct  lies  above  the  lamina  spiralis,  and, 
in  a  section  of  the  cochlea  parallel  to  the  long  axis  of  the  modiolus, 
it  is  of  nearly  triangular  shape,  with  the  somewhat  rounded  apex 
of  the  triangle  attached  to  the  osseous  lamina  spiralis.  In  the 
cochlear  duct  we  may  distinguish  the  following  parts  :  (i)  the  outer 
wall,  which  is  intimately  connected  with  the  periosteum  of  the  bony 
cochlear  canal  ;  (2)  the  tympanal  wall,  resting  on  the  membranous 
basilar  membrane,  with  its  highly  differentiated  neuro-epithelium, 
the  spiral  organ  of  Corti  ;  and  (3)  the  vestibular  wall,  bordering  on 
the  scala  vestibuli,  the  intervening  structures  forming  a  veiy  delicate 
membrane — the  vestibular  or  Reissue r 's  membrane. 

From  the  account  given  thus  far,  it  may  be  seen  that  within  the 
bony  cochlear  canal  there  are  found  three  membranous  canals, 
running  parallel  with  one  another  and  with  the  osseous  lamina  spi- 
ralis about  which  they  are  grouped.  Two  of  these  membranous 
canals,  the  scala  vestibuli  and  the  scala  tympani,  are  perilymphatic 
spaces,  and  are  consequently  lined  by  endothelial  cells  ;  between 
them  is  found  the  cochlear  duct,  from  its  position  known  also  as 
the  scala  media,  lined  by  epithelial  cells.  These  three  membranous 
canals  retain  their  relative  position  in  their  spiral  course  about  the 
modiolus,  and,  in  a  section  through  the  cochlea  parallel  to  the  bony 


THE    INTERNAL    EAR. 


445 


axis  of  the  modiolus,  would  be  met  with  at  each  turn,  and  at  each 
turn  present  essentially  the  same  relative  position  and  structure. 
Figure  348  is  sketched  from  such  a  section,  and  shows  the  appear- 
ance presented  by  a  section  through  one  of  the  turns  of  the  bony 
cochlear  canal  as  well  as  a  section  of  the  contained  osseous  lamina 
spiralis,  the  scalae,  and  the  cochlear  duct.  We  may  now  proceed 
with  a  fuller  consideration  of  the  structures  mentioned. 


Fig.  348. — Section  through  one  of  the  turns  of  the  osseous  and  membranous  coch- 
lear ducts  of  the  cochlea  of  a  guinea-pig  ;  X  9°  :  ?*  Scala  vestibuli ;  m,  labium  vestibu- 
lare  of  the  limbus  ;  «,  sulcus  spiralis  internus  ;  o,  nerve-fibers  lying  in  the  lamina  spi- 
ralis ;  /,  ganglion  cells  ;  q,  blood-vessels  ;  a,  bone  ;  b,  Reissner's  membrane  ;  DC,  ductus 
cochlearis  ;  d,  Corti's  membrane;/,  prominentia  spiralis;  g,  organ  of  Corti ;  h,  liga- 
mentum  spirale  ;  i,  crista  basilaris  ;  /£,  scala  tympani. 

The  lamina  spiralis  ossea  consists  of  two  bony  plates  which  in- 
close between  them  the  ramifications  of  the  cochlear  nerve.  The 
vestibular  surface  of  the  osseous  lamina  spiralis  is  covered  by  peri- 
osteum, which  is  continuous  with  a  peculiar  tissue,  known  as  limbns 
spiralis.  The  latter  begins  at  the  point  of  attachment  of  Reissner's 
membrane,  extends  peripherally  (externally),  and  ends  in  two 
sharp  ridges,  of  which  the  shorter,  the  labium  vestibular e >  projects 


446  THE    ORGAN    OF    HEARING. 

into  the  inner  space  of  the  cochlear  duct  and  continues  into  the 
tectorial  membrane  ;  while  the  other  and  longer,  the  labinm  tym- 
panicum, becomes  attached  to  the  wall  of  the  scala  tympani  and 
continues  into  the  basilar  membrane.  Between  the  two  ridges  is  a 
sulcus,  the  siilcus  spiralis  intcrnus.  (Fig.  348.)  The  limbus  spiralis 
is  a  connective-tissue  formation  in  the  region  of  the  cochlear  duct 
connected  with  the  periosteum  of  the  osseous  spiral  lamina  and 
extending  from  the  point  of  attachment  of  Reissner's  membrane 
to  the  labium  tympanicum.  The  tissue  of  the  limbus  spiralis  is 
dense  and  richly  cellular^  and  simulates  in  its  structure  the  sub- 
stantia  propria  of  the  cornea.  A  casual  view  would  seem  to  disclose 
a  high  columnar  epithelium,  but  upon  closer  observation,  it  is  seen 
that  the  cellular  elements  are  interspersed  with  fibers  which  extend 
to  the  surface.  Some  investigators  regard  this  tissue  as  fibrocar- 
tilage ;  others,  again,  as  a  tissue  sui  generis,  consisting  of  epithelial 
cells  mingled  with  connective-tissue  fibers.  If  the  labium  vestibulare 
of  the  limbus  spiralis  be  examined  from  the  vestibular  surface,  a 
number  of  irregular  tubercles  are  seen  at  its  inner  portion  (near 
Reissner's  membrane),  while  at  its  outer  portion  long,  radially  dis- 
posed ridges  may  be  observed,  the  so-called  auditory  teeth  of 
Huschke.  The  connective-tissue  wall  of  the  sulcus  spiralis  internus 
consists  of  a  nonnucleated  fibrillar  tissue  which  is  continued  into  the 
labium  tympanicum.  The  latter  is  perforated  by  nerves,  thus  giving 
rise  at  this  point  to  the  foramina  nervosa. 

Between  the  point  of  attachment  of  Reissner's  membrane  and 
the  labium  vestibulare,  the  superficial  epithelium  of  the  limbus  spiralis 
is  flat,  and  lines  the  auditory  teeth  and  the  depressions  between 
them  in  a  continuous  layer.  The  epithelium  of  the  sulcus  spiralis 
internus  is  somewhat  higher. 

The  ligamentum  spirale  forms  the  thickened  periosteum  of  the 
outer  wall  of  the  osseous  cochlear  canal.  It  presents  two  inwardly 
projecting  ridges,  the  crista  basilaris,  to  which  the  membranous 
lamina  spiralis  is  attached,  and  the  prominentia  spiralis,  which  con- 
tains one  or  several  blood-vessels  ;  between  the  two  ridges  lies  the 
sulcus  spiralis  externus.  The  portion  of  the  ligamentum  spirale 
forming  the  periosteum  of  the  bony  cochlear  canal  consists  of  a 
fibrous  tissue  containing  many  nuclei,  but  changes  internally  into 
a  looser  connective  tissue.  The  connective  tissue  lying  external  to 
the  outer  wall  of  the  cochlear  duct  is  very  dense  and  rich  in  cellular 
elements  and  blood-vessels,  but  in  the  crista  basilaris  it  changes  to 
a  hyaline,  noncellular  tissue,  continuous  with  the  lamina  basilaris. 
That  portion  of  the  spiral  ligament  lying  between  the  prominentia 
spiralis  and  the  attachment  of  Reissner's  membrane  is  known  as 
the  stria  vascularis.  The  epithelium  covering  this  area  (a  portion 
of  the  epithelium  lining  the  cochlear  duct)  consists  of  cubic, 
darkly  granulated  cells,  which  show  no  distinct  demarcation  from 
the  underlying  connective  tissue,  and  consequently  appear  to  have 
blood-capillaries  extending  into  the  epithelium  itself. 


THE    INTERNAL    EAR.  447 

The  membranous  lamina  spiralis,  or  the  basilar  membrane, 
extends  from  the  tympanic  lip  of  the  osseous  spiral  lamina  to  the 
crista  basilaris  of  the  ligamentum  spirale. 

As  already  stated,  the  tissue  composing  the  labium  tympani- 
cum  of  the  limbus  extends  into  the  basilar  membrane.  In  this 
membrane  the  surface  toward  the  cochlear  duct  is  known  as  the 
cochlear  surface,  that  toward  the  scala  tympani  as  the  tympanic 
surface.  Two  layers  are  differentiated  in  the  basilar  membrane, 
the  lamina  basilaris  propria  and  the  tympanic  investing  layer.  The 
lamina  propria  consists,  in  turn,  of  (i)  radially  arranged  basilar 
fibers,  or  acoustic  strings  ;  (2)  two  thin  strata  of  a  homogeneous 
substance,  one  above  and  the  other  below  the  layer  of  basilar  fibers, 
the  upper  of  which  is  the  thicker  and  nucleated  ;  and  (3)  a  fine  cuti- 
cula,  of  epithelial  origin,  lying  on  the  cochlear  side.  The  tympanic 
investing  layer  is  highly  developed  in  youth,  but  later  becomes 
thinner,  and  may  then  be  differentiated  into  a  connective-tissue 
layer,  regarded  as  a  periosteal  continuation  of  the  tympanic  por- 
tion of  the  osseous  lamina  spiralis,  and  an  endothelial  cell  layer 
belonging  to  the  lining  of  the  perilymphatic  space  or  the  scala 
tympani.  In  the  vicinity  of  the  labium  tympanicum  is  a  blood- 
vessel situated  within  the  tympanic  investing  layer  of  the  basilar 
membrane — the  vas  spirale. 

Reissner's  membrane  consists  of  an  exceedingly  thin  connective- 
tissue  lamella,  lined  on  the  side  of  the  cochlear  duct  by  a  layer  of 
flattened  epithelial  cells  and  on  the  vestibular  side  by  a  layer  of 
endothelial  cells.  The  epithelium  lining  the  cochlear  duct  is  occa- 
sionally raised  into  small  villus-like  projections. 

The  Organ  of  Corti. — In  the  region  of  the  labium  tympan- 
icum of  the  limbus  spiralis  and  in  the  greater  portion  of  the 
adjoining  basilar  membrane,  the  epithelium  of  the  cochlear  duct  is 
peculiarly  modified,  forming  here  a  neuro-epithelium,  which  receives 
the  terminal  ramifications  of  the  cochlear  nerve  and  is  known  as  the 
spiral  organ  of  Corti. 

Passing  from  the  labium  tympanicum  to  the  ligamentum  spirale, 
the  following  three  regions  may  be  recognized  in  the  organ  of 
Corti  :  An  inner  region,  composed  of  the  inner  sustentacular  cells 
and  the  inner  auditory  cells  ;  a  middle  region,  consisting  of  the 
arches  of  Corti  ;  and  an  outer  region,  in  which  are  found  the  outer 
auditory  cells  and  the  outer  sustentacular  cells  or  Deiters's  cells. 
Two  cuticular  membranes  are  in  close  relationship  to  the  organ  of 
Corti  :  namely,  the  lamina  reticularis  and  the  membrana  tectoria,  or 
membrane  of  Corti. 

In  figure  349,  a  sketch  of  the  organ  of  Corti  and  adjacent 
structures,  it  may  be  observed  that  the  epithelium  lining  the  sulcus 
spiralis  internus  (at  the  right  of  the  figure)  is  of  the  pavement 
variety,  and  that  the  epithelium  becomes  gradually  thicker  until  the 
organ  of  Corti  is  reached,  where  it  becomes  suddenly  elevated  in 
the  form  of  a  wall.  In  this,  two  varieties  of  cells  are  distinguished 


448  THE    ORGAN    OF    HEARING. 

— sustentacular  cells  and  inner  auditory  cells.  The  sustentacular 
cells,  which  follow  the  flattened  cells,  become  gradually  higher 
from  within  outward  and  occupy  three  or  four  rows.  Next  come 
the  inner  auditory  cells,  cylindric  elements,  somewhat  rounded  and 
thickened  at  their  nucleated  basilar  ends.  The  latter  do  not  extend 
to  the  basilar  membrane  but  end  at  about  the  level  of  the  center  of 
the  inner  pillars.  At  the  free  end  of  each  cell  is  an  elliptic  cuti- 
cular  zone,  somewhat  broader  than  the  end-surface  of  the  corre- 
sponding cell.  In  man  about  twenty  rigid  filaments,  known  as 
auditory  hairs,  are  found  resting  on  each  elliptic  cuticular  zone. 
These  are  either  -arranged  in  a  straight  row  or  they  describe  a  slight 
curve. 

The  middle  division  of  the  organ  of  Corti,  the  arches  of  Corti, 
consists  of  long  slender  structures,  known  as  pillar  cells,  or,  briefly, 
pillars,  resting  firmly  upon  the  basilar  membrane  and  forming  an 
arch  at  the  vestibular  side  of  the  latter.  They  surround,  by  the 


Fig.  349. — Organ  of  Corti  :  At  x  the  tectorial  membrane  is  raised ;  c,  outer  sus- 
tentacular cells  ;  d,  outer  auditory  cells  ;  f,  outer  pillar  cells  ;  g,  tectorial  membrane  ;  //, 
inner  sustentacular  cells;  ?',/,  epithelium  of  the  sulcus  spiralis  internus  ;  k,  labium  ves- 
tibulare  ;  e,  tympanic  investing  layer  ;  m,  outer  auditory  cells  ;  n,  n,  nerve-fibers  which 
extend  through  the  tunnel  of  Corti ;  o,  inner  pillar  cell ;  q,  nerve-fibers  ;  6,  bt  basilar  mem- 
brane ;  #,  epithelium  of  the  sulcus  spiralis  externus ;  r,  cells  of  Hensen  ;  s,  inner  audi- 
tory cell  ;  /,  ligamentum  spirale  (after  Retzius). 

union  of  their  free  ends,  a  space  which,  as  seen  in  figure  349, 
appears  triangular  in  section.  This  is  the  tunnel  of  Corti. 

According  to  their  position,  we  distinguish  inner  and  outer 
pillars,  the  inner  being  more  numerous  than  the  outer.  Including 
the  entire  extent  of  the  lamina  spiralis  membranacea,  we  find  that 
there  are  about  6000  of  the  inner  and  4500  of  the  outer  pillar  cells. 

Each  pillar  cell  originates  from  an  epithelial  cell,  and  is  found 
to  be  composed  of  a  protoplasmic  portion  containing  the  nucleus, 
which  may  be  regarded  as  a  remnant  of  the  primitive  cell,  and  of  a 
cuticular  formation  derived  from  the  primitive  cell,  forming  the 
elongated  body  of  the  pillar  cell — the  pillar.  The  free  adjoining 
ends  are  called  the  heads  of  t/ie  pillars.  The  head  of  the  inner 
pillar  is  provided  with  a  flattened  process,  the  head-plate,  which 
extends  outward  and  forms  an  obtuse  angle  with  the  axis  of  the 


THE    INTERNAL    EAR.  449 

pillar.  Under  this  plate,  and  at  the  outer  side  of  the  head  of  the 
inner  pillar,  is  a  depression  into  which  fits  the  head  of  the  outer 
pillar.  The  latter  also  extends  outward  in  the  shape  of  a  phalan- 
ge al  plate,  with  a  thinner  process,  the  phalange al  process,  at  its  end. 
The  phalangeal  plate  and  process  lie  under  the  head-plate  of  the 
inner  pillar,  the  process  extending  a  little  beyond  this,  forming  an 
acute  angle  with  the  head  of  the  outer  pillar.  At  the  inner  side 
of  the  head  of  the  outer  pillar  is  a  convex  articular  surface,  with 
which,  as  a  rule,  two,  and  occasionally  even  three,  articular  sur- 
faces of  the  inner  pillars  come  in  contact.  The  outer  and  inner 
pillars  appear  to  possess  an  indistinct  longitudinal  striation,  and 
their  basilar  plates  are  continuous  with  the  extremely  fine  cuticula 
covering  the  basilar  membrane.  The  inner  margins  of  the  basilar 
plates  belonging  to  the  inner  pillars  border  on  the  foramina  ner- 
vosa  ;  while  the  outer  margins  of  the  basilar  plates  belonging  to 
the  outer  pillars  come  in  contact  with  the  basal  end  of  the  inner- 
most row  of  the  cells  of  Deiters  in  the  outer  region  of  Corti's 
organ.  The  protoplasmic  portions  of  the  pillar  cells,  constituting 
what  are  known  as  basal  cells,  lie  against  the  basilar  plates  of  the 
corresponding  pillars, — i.  e.,  on  the  basilar  membrane, — and  partly 
cover  the  bodies  of  the  pillars,  especially  the  surfaces  toward  the 
tunnel. 

In  order  to  comprehend  the  relative  position  of  the  inner  audi- 
tory cells  to  the  inner  pillars,  it  may  be  stated  that  one  auditory 
cell  rests  upon  every  two  inner  pillars. 

The  outer  region  of  Corti's  organ  is  joined  directly  to  the  outer 
pillar  cells,  and  consists  of  four  rows  of  auditory  cells  alternating 
with  an  equal  number  of  sustentacular  cells  or  Deiters's  cells. 
Following  these  structures  and  in  contact  with  them  are  the  outer- 
most sustentacular  cells,  known  as  Hensen's  cells. 

The  outer  auditory  cells  have  a  structure  similar  to  that  of  the 
inner  auditory  cells,  but  possess  a  more  slender  body.  They  do 
not  extend  as  far  as  the  basilar  membrane,  but  end  at  a  distance 
from  the  latter  equal  to  about  double  their  own  length.  The  cutic- 
ular  zone  of  each  outer  auditory  cell  likewise  assumes  the  form  of 
an  ellipse,  with  its  long  axis  pointing  radially.  The  surface  of  this 
zone  also  is  provided  with  about  twenty  stiff  auditory  hairs, 
arranged  in  the  form  of  a  decidedly  convex  arch,  the  convexity  of 
which  points  outward.  At  a  short  distance  from  the  cuticular  zone 
of  each  outer  auditory  cell  is  a  peculiar  round  body,  found  only  in 
these  cells,  the  significance  of  which  is  unknown. 

Deiters's  cells  rest  on  the  basilar  membrane,  and  in  shape  resem- 
ble a  flask  with  a  narrow  neck,  known  as  the  plialangeal  process, 
the  latter  lying  between  the  auditory  cells.  The  nuclei  of  Deiters's 
cells  lie  in  the  upper  parts  of  the  thickened  basal  portions  of  these 
cells. 

With  each  Deiters's  cell  there  is  associated  a  cuticular  structure, 
which  extends  along  the  surface  of  each  cell  in  the  form  of  a  thin 
29 


45O  THE    ORGAN    OF    HEARING. 

fiber,  the  sustentacular  fiber,  and  which  is  found  partly  within  and 
partly  without  the  cell.  The  sustentacular  fiber  begins  near  the 
center  of  the  thicker  basal  portion  of  the  cell-body  and  extends  first 
into  the  cell  itself,  then  passes  to  the  surface,  and,  entering  the 
phalangeal  process,  passes  to  the  top  of  the  cell  and  expands  as  a 
plate,  to  which  the  name  phalangeal  plate  has  been  given.  The 
latter  is  broader  than  the  phalangeal  process,  and  since,  as  we  shall 
see,  the  phalangeal  plates  are  joined  to  one  another,  as  well  as  to 
the  elliptically  shaped  cuticular  zones  of  the  outer  auditory  cells, 
there  remains  a  space  between  the  cells  of  Deiters  and  the  auditory 
cells,  as  also  between  the  outer  pillars  and  the  innermost  of  the 
outer  auditory  cells,  known  as  NueVs  space.  To  the  basal  regions 
of  the  inner  row  of  the  cells  of  Deiters  is  joined  the  basal  plate  of 
the  outer  pillars  of  the  arches  of  Corti. 

Next  to  the  outer  row  of  Deiters's  cells  are  the  cells  of  Hensen, 
arranged  in  about  eight  radially  disposed  rows.  They  form  an 
eminence  which  is  high  internally,  but  gradually  decreases  in  height 
externally.  The  somewhat  narrowed  bases  of  Hensen's  cells  prob- 
ably extend,  without  exception,  to  the  basilar  membrane.  The  free 
surfaces  of  these  cells  are  likewise  covered  by  a  thin  cuticular  mem- 
brane. In  man  the  cells  of  Hensen  usually  contain  yellow  pigment ; 
in  the  guinea-pig,  as  a  rule,  fat ;  and  in  the  rabbit,  generally  rudi- 
ments of  sustentacular  fibers.  Externally  the  cells  of  Hensen  gradu- 
ally change  into  elements  of  a  more  cuboid  type— the  cells  of 
Claudius,  of  which  there  are  about  ten  rows,  radially  disposed.  The 
surfaces  of  the  latter  also  possess  a  cuticular  margin  ;  the  nucleus  is 
at  the  center  of  each  cell  and  pigment  is  also  present.  Darker 
elements  with  more  basally  situated  nuclei  sometimes  occur  be- 
tween these  cells,  giving  rise  to  the  appearance  of  a  double-layered 
epithelium  (Bottcher's  cells). 

Thus  far  we  have  considered  in  detail  the  cells  comprising  the 
organ  of  Corti,  and  described  their  relative  positions  and  sequence 
from  within  outward.  In  order  to  give  a  clearer  understanding  of 
the  mutual  relations  of  these  cells,,  from  within  outward  and  in  the 
direction  of  the  spiral  turning  of  the  cochlea,  we  shall  now  consider 
the  appearance  presented  in  a  surface  view  of  the  organ  of  Corti. 

From  within  outward  a  surface  view  of  the  organ  of  Corti  pre- 
sents the  following  characteristics  :  The  somewhat  broadened  hex- 
agonal outlines  of  the  inner  sustentacular  cells  adjoin  the  epithelial 
elements  of  the  sulcus  spiralis  internus  and  terminate  externally  in 
a  spiral  undulating  line  (if  seen  for  only  a  short  distance,  this  line 
appears  straight).  On  this  line  border  the  contours  of  the  cuticular 
zones  belonging  to  the  inner  auditoiy  cells.  "The  outer  margins  of 
the  cuticular  zones  come  in  contact  with  the  head-plates  of  the 
inner  pillars,  the  cuticular  zone  of  one  inner  auditory  cell  coming  in 
contact  with  at  least  two  head-plates.  The  externally  directed  pro- 
cesses of  the  head-plates  belonging  to  the  inner  pillars  come  in 
contact  with  one  another  and  end  in  a  spiral  line  which  for  a  short 


THE    INTERNAL    EAR. 


451 


3 


distance  is  apparently  straight.  The  head -plates  of  the  inner  pillars 
cover  the  head-plates  of  the  outer  pillars  (which  also  come  in  con- 
tact with  each  other),  also  their  phalangeal  plates,  but  not  their 
phalangeal  processes,  which  thus  pro- 
ject, beyond  the  line  formed  by  the  /  -V. /0"'-- ;  ' -'" ^ 
outer  borders  of  the  head-plates  of 
the  inner  pillars.  It  should  be  men- 
tioned that  about  three  head-plates 
belonging  to  the  inner  pillar  cells  are 
in  apposition  to  every  two  head-plates 
and  their  phalangeal  processes  of  the 
outer  pillar  cells.  The  succeeding 
four  rows,  from  within  outward,  are 
made  up  of  alternately  placed  cutic- 
ular  zones  of  the  outer  hair  cells  and 
the  phalangeal  plates  of  the  Deiters's 
cells,  alternating  like  the  squares  of  a 
chess-board.  This  regular  arrange- 
ment is  lost  in  the  outer  row  of 
Deiters's  cells.  The  cells  of  Hensen 
adjoin  this  row,  and  when  viewed  from 
the  surface,  present  the  appearance  of 
irregular  polygons. 

This  arrangement  is,  however,  sel- 
dom found  to  be  as  typical  as  that 
just  described  ;  although  the  relations 
of  the  cells  to  one  another  always 
correspond  in  general  to  the  forego- 
ing scheme. 

In  the  cupolar  and  vestibular  sacs 
the  neuro-epithelium  changes  into  an 
epithelium  of  an  indifferent  type. 

The  lamina  reticularis  is  formed 
by  the  cementing  together  of  the  pha- 
langeal processes  of  the  outer  pillars 
and  the  phalangeal  plates  of  Deiters's 
cells,  and  is  continued  externally  by  a 
cuticular  membrane  which  covers  the 
cells  of  Hensen  and,  as  a  much  thin- 
ner cuticular  membrane,  extends  over 
the  cells  of  Claudius.  In  this  mem- 
brane there  are  found  three  or  four 
rows  of  small  apertures,  into  which 
the  outer  hair  cells  project. 

The  membrana  tectoria  Cortii  is 
attached   to   the   limbus   spiralis,   but 
becomes  free  at  the  margin  of  the  labium  vestibulare  and  thick- 
ens considerably,   again   becoming    thinner   toward    its    free    end. 


Fig.  350.  —  Surface  of  the  organ 
of  Corti,  with  the  surrounding  struc- 
tures, from  the  basal  turn  of  the 
cochlea  of  a  new-born  child ;  the 
original  drawing  reduced  one-half 
(after  Retzius,  84):  #,  Epithelium 
of  the  sulcus  spiralis  externus ;  l>, 
Hensen' s  cells;  c,  terminal  frame; 
d,  phalanges  ;  ft  outer  auditory  cells; 
g,  flattened  processes  of  the  outer  pil- 
lar cells ;  h,  flattened  processes  of  the 
inner  pillar  cells ;  /,  inner  auditory 
cells  ;  k,  inner  sustentacular  cells  ; 
/,  epithelium  of  the  sulcus  spiralis 
internus  ;  rti,  margin  of  the  labium 
vestibulare ;  n,  epithelium  of  the 
limbus  laminae  spiralis  ;  o,  line  of 
attachment  of  the  membrana  Reiss- 
ued ;  /,  epithelium  of  the  membrana 
Reissneri,  the  latter  inverted. 


452  THE    ORGAN    OF    HEARING. 

Hence  an  inner  attached  and  an  outer  free  zone  may  be  differentiated. 
This  membrane  has  no  nuclei,  and  shows  a  fine  radial  striation. 
Its  free  portion  bridges  over  the  sulcus  spiralis  internus  and  rests 
upon  the  organ  of  Corti.  Its  outer  margin  extends  as  far  as  the 
cells  of  Hensen.  The  development  of  this  membrane  is  not 
thoroughly  understood,  although  it  very  probably  represents  a  dis- 
placed cuticular  formation  belonging  to  the  cells  of  the  limbus 
spiralis.  This  acceptation  has  recently  been  confirmed  (Exner). 

The  auditory  nerve  gives  off,  soon  after  entering  the  internal 
auditory  meatus,  vestibular  branches  to  the  maculae  in  the  utriculus 
and  sacculus  and  to  the  cristae  in  the  semicircular  canals,  and  a 
cochlear  branch,  which  passes  up  through  the  modiolus  in  anasto- 
mosing bony  canals.  From  this  centrally  placed  column  of  nerve- 
fibers,  a  continuous  sheet  of  nerve -fibers,  arranged  in  the  form  of 
anastomosing  bundles,  passes  radially  into  the  osseous  spiral  lamina 
and  thence  to  the  organ  of  Corti.  Near  the  base  of  the  osseous 
spiral  lamina,  along  the  entire  length  of  this  sheet  of  nerve-fibers, 
there  is  situated  in  a  special  bony  canal  a  ganglion,  known  as  the 
spiral  ganglion  of  the  cochlea.  The  ganglion  cells  of  this  ganglion 
are  bipolar,  one  of  the  processes  of  each  cell,  the  dendrite,  extending 
outward  through  the  osseous  spiral  lamina  to  the  organ  of  Corti, 
the  other  process,  the  neuraxis,  passing  through  the  bony  canal  in 
the  modiolus,  through  the  internal  auditory  meatus,  and  thence  to 
the  medulla.  The  dendritic  processes  of  the  nerve-cells  of  the 
spiral  ganglion  form  bundles  of  medullated  nerve-fibers,  which  pass 
outward  within  the  osseous  spiral  lamina,  forming,  in  the  outer  por- 
tion of  the  latter,  a  closely  meshed  plexus,  from  which  small  bundles 
of  nerve-fibers  proceed  through  the  foramina  nervosa  of  the  labium 
tympanicum  to  the  organ  of  Corti  ;  immediately  before  passing 
through  these  foramina,  the  medullated  nerve-fibers  lose  their 
medullary  sheaths  and  neurilemma. 

These  nonmedullated  fibers,  with  or  without  further  dividing,  are 
then  arranged  in  small  bundles,  which,  for  a  certain  distance, 
have  a  spiral  course  :  that  is  to  say,  parallel  to  the  tunnel  of  Corti. 
One  such  spiral  bundle  is  situated  on  the  inner  side  of  the  inner 
pillars,  under  the  inner  row  of  hair  cells  ;  another,  on  the  outer  side 
of  the  inner  pillars,  in  the  tunnel  of  Corti.  Other  fibers  pass 
through  the  tunnel  of  Corti,  so-called  tunnel-fibers,  to  reach  the 
outer  side  of  the  arches  of  Corti,  where  they  are  arranged  in  three  or 
four  spiral  bundles,  at  the  outer  side  of  the  outer  pillars  and  between 
the  rows  of  the  cells  of  Deiters.  From  the  nerve-fibers  of  these 
spirally  arranged  bundles,  terminal  branches  are  given  off,  which 
terminate,  after  further  division,  on  the  inner  and  outer  hair  cells. 

Regarding  the  blood-vessels  of  the  membranous  labyrinth,  it 
should  be  mentioned  that  the  internal  auditory  artery  is  a  branch  of 
the  basilar  artery,  and  divides  into  the  rami  vcstihulares  and  rami 
cochleares.  The  branches  of  the  former  accompany  those  of  the 
auditory  nerve  as  far  as  the  utriculus  and  sacculus.  At  the  maculae 


THE    INTERNAL    EAR.  453 

and  cristae  the  capillary  networks  are  numerous  and  finely  meshed, 
but  in  the  remaining  portions  of  the  utriculus,  sacculus,  and  semi- 
circular canals,  they  form  coarser  networks.  The  cochlear  branch 
accompanies  the  divisions  of  the  auditory  nerve  as  far  as  the  first 
spiral  turn  of  the  cochlea  ;  the  arteries  supplying  the  remaining 
turns  enter  the  axis  of  the  modiolus,  where  they  divide  into 
numerous  branches.  The  latter  are  coiled  in  a  peculiar  manner, 
forming  the  so-called  glomeruli  arteriosi  cochlea.  From  these, 
branches  are  given  off  which  penetrate  the  vestibular  wall  of  the 
lamina  spiralis  ossea,  where  they  supply  the  limbus  spiralis  and  the , 
small  quantity  of  connective  tissue  in  the  membrana  vestibularis. 
Other  branches  surround  the  scala  vestibuli,  supply  the  walls  of  the 
latter,  and  then  continue  to  the  ligamentum  spirale,  the  stria  vascu- 
laris,  and  the  lamina  basilaris. 


Fig-  351.— Scheme  of  distribution  of  blood-vessels  in  labyrinth  (after  Eichler) : 
g,  Artery ;  h,  spiral  ganglion  ;  i,  vein  ;  v,  scala  vestibuli ;  DC,  ductus  cochlearis  ;  <-,  cap- 
illaries in  the  ligamentum  spirale  ;  dt  capillaries  in  the  limbus  spiralis;  f,  scala  tympani. 

The  venous  trunks  lie  close  to  the  arteries  and  receive  their 
blood  from  the  veins  which  lie  at  the  tympanal  surface  of  the  lamina 
spiralis  and  from  those  which  encircle  the  outer  wall  of  the  scala 
tympani.  The  former,  in  turn,  receive  their  blood  from  the  capil- 
laries of  the  limbus  spiralis  ;  the  latter,  principally  from  the  region 
of  the  ligamentum  spirale  and  the  basilar  membrane. 

From  this  description  it  is  seen  that  the  arterial  channels  are 
connected  with  the  scala  vestibuli,  the  venous  with  the  scala  tym- 
pani, and  that  the  inner  blood  stream  circulating  through  the  lamina 
spiralis  and  limbus  spiralis  is  separated  from  the  blood  current  of  the 
two  scalae,  the  ligamentum  spirale,  and  the  crista  basilaris  (Eichler). 

The  entire  membranous  labyrinth  is  filled  with  endolymph.  The 
ductus  endolymphaticus  is,  as  will  be  remembered,  a  canal  ending 


454  THE    ORGAN    OF    HEARING. 

under  the  dura  in  a  saccus  endolympliaticus.  In  connection  with 
the  latter  are  epithelial  tubules  bordering  upon  lymph-channels, 
with  which  they  probably  communicate  by  means  of  interepithelial 
(intercellular)  spaces  (Riidinger,  88).  The  efferent  channels  for 
the  perilymph  of  the  vestibule  extend  along  the  nerve  sheaths  of 
those  nerves  supplying  the  maculae  and  cristae  ;  these  passageways 
finally  communicate  with  the  subdural  or  subarachnoid  spaces. 
The  perilymph  of  the  cochlea  is  carried  off  by  the  adventitious 
tissue  of  the  vena  aqueductus  cochleae,  the  lymph-vessels  of  which 
empty  into  certain  subperiosteal  lymph-channels  near  the  inner 
margin  of  the  jugular  fossa. 


4.  ON  THE  DEVELOPMENT  OF  THE  LABYRINTH. 

In  man  the  epithelium  lining  the  membranous  labyrinth  origi- 
nates from  the  ectoderm  as  a  single-layered  epithelial  vesicle,  the 
auditory  vesicle  or  the  otocyst,  during  the  fourth  week  of  embryonic 
life.  After  being  constricted  off  from  the  ectoderm,  this  vesicle 
lies  in  the  vicinity  of  the  epencephalon  and  is  surrounded  by  mesen- 
chyme.  The  auditory  vesicle  then  develops  a  dorsomesial  evagina- 
tion,  which  gradually  grows  larger  and  finally  becomes  the  ductus 
endolymphaticus.  An  evagination  also  occurs  in  the  ventral  wall 
of  the  vesicle,  the  recessus  cochlea.  At  the  same  time  the  mesial 
wall  is  pushed  inward,  thus  incompletely  dividing  the  vesicle  into 
two  smaller  sacs — the  dorsal  iitricidus  and  the  ventral  sacculus. 
From  the  utricular  portion  there  arises  a  horizontal  evagination, 
flat  and  quite  broad — the  first  trace  of  the  lateral  or  horizontal 
semicircular  canal  ;  soon  after,  another  evagination,  vertical  and 
still  broader  than  the  first,  is  seen — -the  anlage  of  the  other  two 
canals.  The  outer  portion  of  these  pouches  gradually  expands, 
while  in  the  middle,  the  two  layers  of  each  evagination  come  in 
contact  with  each  other  and  coalesce,  finally  becoming  absorbed. 
In  the  vertical  evagination  two  such  areas  of  adherence  are  found, 
thus  forming  a  superior  and  a  posterior  canal,  both  having  a  com- 
mon crus  at  one  end. 

The  recessus  cochleae  grows  both  in  a  longitudinal  and  in  a  spiral 
direction,  forming  the  cochlear  duct. 

In  the  immediate  vicinity  of  the  membranous  labyrinth,  the 
mesenchyme  is  differentiated  into  a  connective -tissue  wall  for  the 
former.  The  successive  layers  of  mesenchyme,  except  in  those 
areas  where  the  membranous  labyrinth  later  becomes  adherent  to 
the  osseous,  are  transformed  into  a  mucous  connective  tissue.  The 
latter  is  surrounded  by  a  more  compact  tissue,  from  which  are  de- 
rived, first,  cartilage  ;  then  bone  and  periosteum,  and  thus,  finally, 
the  osseous  labyrinth.  By  a  peculiar  process  of  regressive  meta- 
morphosis most  of  the  mucous  connective  tissue  later  disappears. 
In  the.  adult  it  is  replaced  by  the  perilymphatic  spaces  of  the  laby- 
rinth (compare  Retzius,  84 ;  Schwalbe,  87). 


TECHNIC.  455 

TECHNIC 

329.  In  the  treatment   of  the    external  and  middle  ear  the  usual 
methods  are  employed.     For  the  study  of  the  epithelium  in  conjunction 
with  the  adjacent  bone  the  tissue  is  fixed  and  then  decalcified,  or  sub- 
jected to  those  fixing  methods  which  accomplish  both  processes  at  the 
same  time.     The  latter  method,  however,  can   be  applied  only  to  very 
small  objects. 

330.  The  manipulation  of  the  membranous  labyrinth,  especially  that 
of  the  adult,  is  a  very  difficult  technical  problem.     Its  isolation  from  the 
petrous  portion  of  the  temporal  bone  without  injury  can  be  accomplished 
only  in  well -advanced  fetuses  and  in  children,  and  even  here  a  thorough 
knowledge  of  the  situation  of  the  parts  in  the  petrous  portion  of  the  tem- 
poral bone  is  essential.     Smaller  animals,  especially  rodents,  afford  better 
specimens.     In  the  latter,  the  semicircular  canals  and  cochlea  give  rise  to 
more  or  less  distinct  projections  into  the  tympanic  cavity.      If  the  latter 
be  opened,  the  situation  of  the  parts  may  be  ascertained  from  without.    In 
the  rabbit  and  guinea-pig,  the  entire  cochlea  projects  into  the  tympanic 
cavity,  and  may  be  easily  removed  in  toto  with  a  strong  knife,  and,  as 
the  bony  cochlea  in  these  animals  has  very  thin  walls,  it  offers  very  little 
resistance  to  the  decalcifying  fluid  (use,  for  instance,  3%  nitric  acid). 

331.  According  to  Ranvier's  method  (89),  the  cochlea  is  opened  with 
a  scalpel  in  a  2  %  solution  of  osmic  acid  in  normal  salt  solution.     After 
twelve  hours  the  cochlea  is  placed  for  decalcification  in  2  %  chromic  acid, 
which  is  frequently  changed.     In  guinea-pigs,  for  instance,  decalcification 
is  accomplished  in  a  week. 

332.  According  to  the  method  of  Retzius  (84),  the  opened  cochlea  is 
treated  for  half  an  hour  with  a  0.5%  aqueous  solution  of  osmic  acid,  and 
then  for  the  same  length  of  time  with  a  0.5%  aqueous  solution  of  gold 
chlorid.      The  organ  of  Corti  is  then  dissected  out  and  examined  as  a 
whole,  or  cut  after  carefully  removing  the  bone. 

333.  The  labyrinth  of  the  human  adult  is  usually  prepared  as  follows  : 
The  apex  of  the  petrous  portion  of  the  temporal  bone  is  removed  and  the 
upper  semicircular  canal,  together  with  the  cochlea,  opened  in  Miiller's 
fluid  ;  in  this  solution  the  pyramid  is  left  for  three  weeks  ;  during  the  first 
week  the  fluid  is  changed  daily,  and  every  two  days  during  the  following 
weeks.     The  specimen  is  then  washed  for  twenty-four  hours  in  running 
water,  placed  in  80%  alcohol  for  two  weeks,  and  finally  in  96%  alcohol 
for  two  days.     The  preparation  is  now  ready  for  decalcification.     This  is 
done  with  5%  nitric  acid,  which  is  to  be  changed  daily  (ten  days  to  two 
weeks).     Then  follows  washing  for  two  days  in  running  water,  carrying 
over  into  80%  alcohol  for  twenty-four  hours,  then  into  96%  alcohol  for 
from  six  to  eight  days,  and,  finally,  infiltration  and  imbedding  in  cel- 
loidin  (A.  Scheibe). 

334.  The  following  method  may  also  be  employed  with  good  results  : 
The    isolated   pyramid  with  opened   semicircular   canal  and    cochlea  is 
treated  with  Miiller's  fluid  for  two  days  at  room -temperature,  and  then 
for  three  weeks  in  a  thermostat  at  23°  C.      During  the  latter  period,  the 
fluid  should  be  changed.     The  specimen  is  then  washed  for  forty-eight 
hours  in  running  water,  treated  for  fourteen  days  with  80%  alcohol,  then 
for  eight  days  with  96%  alcohol,  decalcified,  and  further  treated  as  in 
the  preceding  method. 


456  THE    ORGAN    OF    SMELL. 

335.  Up  to  the  present  time  it  has  been  customary  to  cut  sections  in 
celloidin  ;  but  the  combined  celloidin -paraffin  method  may  also  be  em- 
ployed with  good  results,  and  even  the  paraffin  method,  if  great  care  be 
exercised  in  imbedding  the  tissue. 

336.  The    nerve-fibers  and   nerve-endings   of  the   cochlea    may  be 
stained  with  the  chrome-silver  method.      For  this  purpose  it  is  recom- 
mended to  employ  embryos  or  young  fetuses. 


X.  THE  ORGAN    OF   SMELL 

THE  nasal  cavity  consists  of  the  vestibule,  the  respiratory  region 
with  the  accessory  cavities,  and  the  olfactory  region. 

The  vestibule  is  lined  by  stratified  squamous  epithelium.  In 
the  region  of  the  anterior  nares  are  hairs,  the  sebaceous  glands  of 
which  are  markedly  developed,  while  at  the  level  of  the  cartilage 
mucous  glands  are  also  present.  The  stratified  squamous  epithe- 
lium ceases  at  the  anterior  end  of  the  inner  turbinate  bone  and  at 
the  inferior  nasal  duct. 

The  respiratory  region  possesses  a  simple  pseudostratified, 
ciliated  epithelium  having  two  strata  of  nuclei  and  provided  with 
goblet  cells  ;  the  direction  of  the  ciliate  movement  is  toward  the 
posterior  nares.  Numerous  leucocytes  are  usually  found  in  the 
epithelium  and  in  the  underlying  mucosa.  Branched  alveolar 
glands,  having  mucous  and  serous  alveoli,  are  here  present.  Within 
the  mucosa  are  highly  developed  vascular  plexuses,  more  especially 
of  a  venous  character.  The  accessory  cavities  are  likewise  lined 
by  ciliated  epithelium,  the  ciliate  movement  being  directed  exter- 
nally. 

The  olfactory  region  is  principally  confined  to  the  superior  tur- 
binate bone  and  to  the  nasal  septum  lying  opposite,  although  in 
the  immediate  vicinity  of  the  olfactory  region  a  few  small  islands  of 
the  same  epithelial  type  are  found,  either  entirely  isolated  or  con- 
nected with  the  principal  region  by  narrow  bridges.  In  a  fresh 
condition  the  olfactory  region  may  be  differentiated  from  the  sur- 
rounding tissue  by  its  color,  which  is  distinctly  yellow  in  man. 
Its  pigment  is  contained  within  the  sustentacular  cells  described 
on  the  next  page. 

The  epithelium  of  the  olfactory  region  is  of  the  columnar  pseudo- 
stratified type,  with  several  strata  of  nuclei,  and  consequently 
closely  simulates  a  stratified  columnar  epithelium.  Here  we  dis- 
tinguish olfactory  cells  and  sustentacular  cells. 

The  olfactory  cells  occupy  a  peculiar  position  among  the  cells 
of  special  sense  in  that  they  represent  true  ganglion  cells  (von 
Lenhossek).  Within  the  epithelial  layer  they  appear  as  spindle- 
shaped  cells,  with  a  spheric  nucleus  provided  with  a  large  nucleolus 
lying  in  the  thickest  portion  of  each  cell.  The  nuclei  of  the  different 
cells  lie  at  varying  levels  in  the  middle  stratum  of  the  epithelial 


TECHNIC.  457 

layer.  Toward  the  nasal  cavity,  the  cells  terminate  in  blunt  cones, 
upon  each  of  which  are  several  stiff  hairs,  the  olfactory  hairs.  The 
basilar  ends  form  true  centripetal  nerve-processes,  neuraxes,  which 
end  in  the  peculiar  telodendria  constituting  the  glomeruli  of  the 
olfactory  bulb.  (See  p.  379.) 

The  nuclei  of  the  sustentacular  cells  are  more  oval  and  are 
situated  at  nearly  the  same  level.  Toward  the  surface,  each  cell  is 
provided  with  a  narrow  cuticular  zone,  while  toward  the  basement 
membrane,  it  terminates  in  two  or  more  pedicles.  Between  the 
basilar  ends  of  these  cells  we  find  a  layer  of  elements  the  broad 
nucleated  bodies  of  which  rest  on  the  basement  membrane,  while 
their  upper  extremities  terminate  in  short  superficial  processes. 

The  mucosa  contains  a  large  number  of  leucocytes  as  well  as 
numerous  branched  alveolar  glands,  the  so-called  glands  of  Bow- 
ma)!.  In  man  these  are  albuminous  (serous)  glands,  and  their 
ceils  sometimes  contain  pigment. 

Jacobson's  organ  contains  no  typical  olfactory  cells  in  the  human 
being. 

The  capillaries  spread  out  immediately  beneath  the  basement 
membrane  of  the  epithelium.  In  the  submucous  connective 
tissue,  we  find  a  relatively  well  developed  vascular  plexus,  rich  in 
venous  vessels  ;  this  plexus  is  especially  marked  at  the  posterior 
portion  of  the  inferior  turbinate  bone,  forming  here  a  tissue  which 
resembles  erectile  tissue. 

A  dense  network  of  lymphatics  ramifies  throughout  the  mucous 
membrane,  carrying  the  lymph  to  the  pharynx  and  palate.  These 
lymph-vessels  may  be  injected  through  the  subarachnoid  space 
(Key  and  Retzius). 

The  nerves  (trigeminal)  are  widely  distributed  in  the  epithelium, 
ramifying  through  both  the  respiratory  and  olfactory  regions. 
After  repeated  divisions  these  nerves  lose  their  medullary  sheaths, 
and  end  in  telodendria  which  are  usually  provided  with  terminal 
nodules,  although  some  are  found  which  end  in  mere  filaments. 


TECHNIC, 

337.  The  nasal  mucous  membrane  is  fixed  in  situ  with  osmic  acid  or 
one  of  its  mixtures,  after  which  small  pieces  are  removed.      It  should  be 
mentioned  that  the  nonmedullated  fibers  of  the  olfactory  nerve  assume  a 
brownish  color  under  this  treatment,  while  the  fibers  of  Remak  do  not 
(Ranvier,  89). 

338.  In  order  to  isolate  the  epithelial  elements,  pieces  of  the  mucous 
membrane  are  treated  with  the  ^  alcohol  of  Ranvier.     But  since  the 
prolongations  of  the  olfactory  cells  (neuraxes)  shrivel  and  curl  in  this 
fluid,    Ranvier  recommends   that,   after   the   epithelial    cells   have  been 
macerated  in  y$  alcohol  for  one  or  two  hours,  they  be  treated  with  i  % 
osmic  acid  for  a  quarter  of  an  hour.      If  shreds  be  now  placed  in  water 
and  teased,  the  cells,  together  with  their  prolongations,  may  be  isolated 
without  the  curling  of  the  latter. 


GENERAL    CONSIDERATION   OF    THE    SPECIAL    SENSE-ORGANS. 

339.  The  chrome-silver  method  applied  to  the  nasal  mucous  membrane 
of  young  animals  and  fetuses  has  been  the  means  of  establishing  the 
important  fact  that  the  olfactory  cells  of  the  olfactory  region  are  in  reality 
peripherally  situated  ganglion  cells. 


XI.  GENERAL  CONSIDERATION   OF  THE  SPECIAL 
SENSE-ORGANS. 

THE  special  sense-organs  present,  in  their  fully  developed  condi- 
tion, a  very  complicated  structure,  and  not  until  quite  recently  has 
it  been  possible  to  demonstrate  any  relationship  existing  between 
them,  nor  has  it  been  possible  to  reduce  them  to  simple  schemata. 
Within  recent  years,  however,  the  researches  of  a  number  of  prom- 
inent investigators  have  enabled  us  to  study  all  the  special  sense- 
organs  from  a  common  point  of  view.  As  is  generally  the  case,  the 
primitive  conditions,  both  ontogenetic  and  phylogenetic,  have  aided 
materially  in  the  comprehension  of  structures  which  later  become 
extremely  complicated. 

Thus,  von  Lenhossek  (92,  i)  has  shown  that  in  the  earth-worm 
(Lumbricus)  certain  cells  occur  between  the  elements  of  the  single- 
layered  epidermis  which  functionate  as  ganglion  cells  :  i.  ^.,  possess 
a  basilar  centripetal  process  simulating  a  neuraxis  in  its  relations  to 
the  central  nervous  system  (in  this  case  the  funiculus  abdominalis) ; 
the  telodendria  of  this  neuraxis  come  in  contact  with  the  dendrites 
of  the  funicular  cells  by  means  of  terminal  ramifications.  Here, 
therefore,  we  have  a  peripherally  situated  ganglion  cell  which,  after 
receiving  an  impulse,  transmits  it  to  the  central  organ.  This  is  the 
simplest  structural  condition  by  means  of  which  an  external  impres- 
sion may  be  transmitted  to  the  central  organ. 

A  slight  modification  of  this  occurs  when  the  ganglion  cell  is 
withdrawn  to  some  extent  below  the  epidermal  layer,  leaving  behind 
it  a  peripherally  directed  process  still  in  contact  with  the  epithelial 
elements.  The  external  impression  is  then  first  taken  up  by  this 
process,  passed  to  the  cell-body,  and  then  to  the  central  organ  by 
means  of  the  neuraxis  of  the  cell.  Here  the  peripheral  process  of 
the  cell  (cellulipetal  process)  may  be  compared  to  a  dendrite.  This 
condition  prevails  in  other  annelids  (Nereis). 

In  the  olfactory  organ  of  the  higher  vertebrates  the  primitive 
structure  is  retained.  Thus,  in  the  nasal  mucous  membrane,  the 
olfactory  cells  must  be  regarded  as  peripheral  ganglion  cells,  since 
they  give  off  neuraxes  the  telodendria  of  which  come  in  contact 
with  the  dendritic  processes  of  the  mitral  cells  in  the  glomeruli 
olfactorii. 

Even  if  we  look  upon  the  epidermal  cells  of  the  skin  as  ele- 
ments not  specially  adapted  to  the  reception  of  an  impression,  we 
are  still  confronted  with  relations  similar  to  those  in  Nereis,  with 


GENERAL    CONSIDERATION    OF    THE    SPECIAL    SENSE-ORGANS.       459 

the  difference  that  in  this  case  the  ganglion  cell  receiving  the  im- 
pression is  removed  a  long  distance  from  the  surface,  lying  in  the 
spinal  ganglion,  but  possessing  a  dendrite  ramifying  within  the 
epidermis. 

When  the  relations  are  such  that  the  nerve-cell,  through  its 
terminations,  not  only  receives  the  physical  impression  from  without, 
but  also  transmits  it  as  a  nerve-impulse  centripetally,  the  special 
sense-organ  may  be  regarded  as  of  the  primary  type.  But  if  certain 
structures  are  found  in  the  external  epithelium  which  transmute  the 
physical  impression  into  impulses  which  are  then  transmitted,  the 
special  sense-organ  becomes  one  which  may  be  looked  upon  as 
secondary  in  type.  In  the  latter  case  the  ganglion  cell  first  receiv- 
ing the  impression  becomes  merely  a  conducting  apparatus,  since 
by  means  of  its  dendrites  it  comes  in  contact  with  a  cell  of  special 
sense,  neuro-epithelial  cell,  developed  from  an  epithelial  cell.  Such 
an  arrangement  exists  in  the  higher  organs  of  special  sense,  in  the 
organs  of  taste,  hearing,  and  sight.  In  the  first,  the  terminal  rami- 
fications of  the  dendrites  of  the  nerve-cells  belonging  to  the  glosso- 
pharyngeal  nerve  come  in  contact  with  the  special  sense  cells,  the 
gustatory  cells,  in  the  taste-buds.  In  the  cochlea,  as  also  in  the 
ampullae,  it  may  be  assumed  that  the  dendrites  from  the  auditory 
ganglion  encircle  the  auditory  cells  (cells  of  special  sense).  In 
other  words,  the  cells  of  the  glossopharyngeal  and  auditory 
ganglia  conduct  the  respective  impressions  to  centrally  placed 
neurones. 

Some  difficulty  is  encountered  in  considering  the  retina ;  this 
may  be  best  overcome  by  regarding  the  visual  cells  as  the  cells  of 
special  sense  which  receive  the  impression,  and  the  bipolar  cells  of 
the  inner  granular  layer  as  the  conducting  elements.  The  cells  of 
the  nerve-cell  layer  of  the  retina  may,  therefore,  be  regarded  as  the 
cells  lying  nearest  to  the  central  organ  (compare  Retzius,  92,  2). 


REFERENCES  TO   LITERATURE 


The  following  list  includes  the  titles  of  articles  and  works  referred  to  in  the  text. 
Authors'  names,  arranged  in  alphabetic  order,  are  followed  by  the  date  of  publication  of 
the  works  referred  to,  the  two  last  figures  of  the  year  of  publication  alone  being  given. 
If  reference  has  been  made  to  more  than  one  of  an  author' s  publications  appearing  in  the 
same  year,  the  date  is  followed  by  a  single  number  to  designate  this  fact.  In  this  respect 
we  follow  Minot,  94.  The  abbreviation  of  titles  of  journals  here  followed  is  the  same  as 
that  in  use  in  the  "  Zoologischen  Jahresbericht." 

Affanassiew,  M.,  84,  Ueber  den  dritten  Formbestandtheil  des  Blutes  in  normalen 
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chen.,  Bd.  i,  2.  Heft,  S.  556-592,  T.  15. 

Altmann,  R.,  79,  Ueber  die  Verwerthbarkeit  der  Corrosion  in  der  mikroskopischen 
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Andres,  A. ,  W.  Giesbrecht,  und  P.  Mayer,  83,  Neuerungen  in  der  Schneidetechnik, 

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in  ibid. ,  Bd.  vn,  S.  742-748. 

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Arnold,  Julius,  83,  Beobachtungen  tiber  Keim-  und  Kerntheilungen  in  den  Zellen  des 
Knochenmarkes,  in  Arch.  path.  Anat.,  Bd.  XLIII,  S.  I. 

—  87,  Ueber  Theilungsvorgange  an  den  Wanderzellen,  ihre  progressiven  und  regres- 
siven  Metamorphosen,  in  Arch.  mikr.  Anat.,  Bd.  xxx,  S.  205-310,  T.  12-16. 

—  96,  Zur  Morphologic  und  Biologic  der  rothen  Blutkorperchen,  in  Arch.  path.  Anat, 
Bd.  CXLV,  S.  1-29,  T.  1-2. 

Arnstein,  95,  Zur  Morphologic  der  sekretorischen  Nervenendapparate,  Anat.  Anzeig., 
Bd.  x,  S.  410. 

Auerbach,  L.,  90,  Ueber  die  Blutkorperchen  der  Batrachier,  in  Anat.  Anzeiger., 
5.  Jahrg.,  S.  570-578,  2  Fig. 

Balfour,  F.  M.     Vergl.  Foster. 

Ballowitz,  E.,  88,  Untersuchungen  uber  die  Struktur  der  Spermatozoen,  zugleich  ein 
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—  90,  2,  Untersuchungen  uber  die  Struktur  der  Spermatozoen,  3.  Fische,  Amphibien, 
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—  91,  Weitere  Beobachtungen  tiber  den  feineren  Bau  der  Saugethier-Spermatozoen,  in 
Zeit.  Wiss.  Z.,  Bd.  LII,  S.  217-293,  T.  13-15. 

461 


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30 


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—  94,  Untersuchungen  iiber  den  feineren  Bau  des  centralen  und  peripherischen  Nerven- 
systems,  S.  1-272,  30  T.,  Deutsch  v.  R.  Teuscher,  Jena  (entha.lt  sammtliche  Unter- 
suchungen Golgi' s  iiber  das  obige  Thema  seit  1871). 

Golubew,  W.  Z.,  93,  Ueber  die  Blutgefasse  in  der  Niere  der  Saugethiere  und  des 

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vergleichenden  Anatomic  des  Saugethierkehlkopfes,  in  Morph.  Jahrb.,  Bd.  xxi,  S. 

68-151,  T.  3  und  4,  13  Textfig. 
Gotte,  Alexander,  68,  Zur  Morphologic  der  Haare,  in  Arch,  mikr,  Anat.,  Bd.  IV,  S. 

273-322,  T.  19,  20. 
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in  Arch.  mikr.  Anat.,  Bd.  xvi,  S.  463-471. 

Griinstein,  99,  Zur  Innervation  der  Harnblase,  Arch.  mikr.  Anat.,  Bd.  LV. 
Gscheidlen,    Richard,  76-79,  Physiologische    Methodik,   Ein  Handbuch  der  prak- 

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Haeckel,  Heinrich,  94.     Vergl.  Bardeleben. 
Halliburton,  W.  D.,  93,   Lehrbuch  der  chemischen  Physiologic  und  Pathologic,  S. 

xn  und  1-883,  104  Fig.,  Deutsch  von  K.  Kaiser,  Heidelberg. 
Hamburger,  Ove,  90,  Ueber  die  Entwickelung  der  Saugethierniere,  in  Arch.  Anat.  u. 

Phys.,  Anat.  Abth.,  Suppl.  Bd.,  S.  15-51,  T.  3,  4. 

Hammer,  Bernh.,  91,  Ueber  das  Verhalten  von  Kerntheilungsfiguren  in  der  mensch- 
lichen Leiche,  Inaug.-Diss.,  Berlin,  39  Sn. 
Harz,  W.,  83,  Beitrage  zur  Histologie  des  Ovariums  der  Saugethiere,  in  Arch.  mikr. 

Anat.,  Bd.  xxn,  S.  374-407,  T.  15. 
Hayem,  Georges,  89,    Du  sang   et   de   ses   alterations   anatomiques,  pp.  xxvi   und 

1-1035,  I26  Fig-.  Paris. 
Heidenhain,  M.,  92,  I,  Ueber  die  Riesenzellen  des  Knochenmarkes  und  ihre  Cen- 

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468  REFERENCES    TO    LITERATURE. 

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Held,  Hans,  97,  Beitrage  zur  Struktur  der  Nervenzellen  und  ihrer  Fortsatze,  in  Arch. 

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—  89,  I,  Beitrage  zur  Histologie  des  Hodens,  in  Arch.  mikr.  Anat.,  Bd.  xxxiv,  S.  58- 
106,  T.  3,  4. 

—  89,  2,  Die  postfotale  Histiogenese  des  Hodens  der  Maus,  in  ibid.,  xxxiv,  S.  429- 
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—  93,  2,  Technik.  Methoden  zum  Studium  des  Archiplasmas  und  der  Centrosomen 
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—  97,  Beitrage  zur  Kenntniss  der  Spermatogenese,  in  Arch.  mikr.  Anat.,  Bd.  L,  S. 
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Hertwig,  O.,  77,  78,  Beitrage  zur  Kenntniss  der  Bildung,  Befruchtung,  und  Theilung 
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—  90,  Vergleich  der  Ei-  und  Samenbildung  bei  Nematoden,  Eine  Grundlage  fur  cel- 
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—  93,  Die  Zelle  und  die  Gewebe,  Grundziige  der  allgemeinen  Anatomic  und  Phy- 
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—  96,  Lehrbuch  der  Entwickelungsgeschichte  des  Menschen  und  der  Wirbelthiere,  S. 
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Hertwig,  O.  und  R.,  8l,  Die  Coelomtheorie,  Versuch  einer  Erklarung  des  mittleren 
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—  89,  Ueber  den  Nachweis  der  Gallenkapillaren  und  spezifischen  Fasern  in  den  Le- 
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—  90,  Die  Entwickelung  von  Petromyzon  Planeri,  in  Arch.  mikr.  Anat.,  Bd.  xxxv, 
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—  92,  Ueber  die  Entwickelung  von    Milz  und  Pankreas,  in  Munch,   med.  Abh.,  7. 
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—  96,    Ueber    Energiden    und    paraplastische    Bildungen,    Rektoratsrede   Univers. 
Munchen,  29  Sn. 

—  99,  Ueber  die  sogenannten  Sternzellen  der  Saugethierleber,  Archiv  mikr.  Anat., 
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Kytmanow,  K.  A.,  96,  Ueber  die  Nervenendigungen  in  den  Labdrusen  des  Magens 
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Landauer,  Armin,  95,  Ueber  die  Struktur  des  Nierenepilhels,  in  Anal.  Anzeiger,  Bd. 
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Langendorff,  O.,  89,  Beilrage  zur  Kennlniss  der  Schilddriise,  in  Arch.  Anal.  u. 
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47 2  REFERENCES  TO  LITERATURE. 

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Lewaschew,  S.  W.,  86,  Ueber  eine  eigenthumliche  Veranderung  der  Pankreaszellen 

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Ber.  Akad.  Wien,  Bd.  xcvi,  3.  Abth.,  S.  184-210,  2  T. 
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Martin,  A.,  89,  I,  Tubenkrankheiten,  in  Real-Encyklopadie  ges.  Heilk.,  Eulenburg, 
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—  89,  2,  Uterus,  in  ibid.,  S.  438-532,  17  Fig. 

Maurer,  F.,  90,  Die  erste  Anlage  der  Milz  und  das  erste  Auftreten  von  lymphatischen 
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Mayer,  Paul,  8l,  Ueber  die  in  der  zoologischen  Station  zu  Neapel  gebrauchlichen 
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Mertsching,  A.,  87,  Beitrage  zur  Histologie  des  Haares  und  des  Haarbalges,  in  Arch. 

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Meynert,  Th.,  72,  Vom  Gehirne  der  Saugethiere,  in  Handb.  Lehre  von  den  Geweben, 

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476  REFERENCES   TO    LITERATURE. 

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—  94,  2,  Les  nouvelles  idees  sur  la  Structure  du  systeme  nerveux  chez  1'homme  et 
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Ranvier,  L.,  75,  Des  preparations  du  tissu  osseux  avec  le  bleu  d' aniline  insoluble  dans 
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72,  2,  Die  Ohrtrompete,  in  ibid.,  S.  867-881,  9  Fig.,  Leipzig. 

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S.  447-461,  T.  22. 

StOSS,  A.,  91,  Konstruktion  eines  Kiihlmessers,  in  Zeitschr.  Wiss.  Mikroskopie,  Bd. 

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Strasburger,  Eduard,  84,  Die  Kontroversen  der  indirekten  Kerntheilung,  in  Arch. 

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INDEX. 


ABBE'S  apparatus,  19 

Absorption  of  fat  by  intestine,  256 

Accessory  disc  of  Engelmann,  127 

thread  of  spermatosome,  323 
Acervulus,  381 

Acetate  of  potash,  mounting  in,  47 
Acetic  acid,  action  of,  on  connective  tissue, 
118 

sublimate  solution  as  fixing  fluid,  24 
Achromatic  portion  of  nucleus,  55 

spindle,  62 
Acid  stains,  40 

Acidophile  cells,    187.      See   also   Cells, 
eosinophile. 

granules,  technic  of,  205 
Adipose  tissue,  99 
Agminated  lymph -nodules,  177 
Akrosome,  339 
Alcohol  as  fixing  solution,  22 
Altmann's  method  of  demonstrating  gran- 
ules in  cells,  72 
of  mounting,  71 

process  of  injection,  149 
Alum-carmin  as  stain,  41 
Alveolar  ducts,  279 

glands,  84 
Alveoli,  84 

of  glands,  84 

of  lungs,  280 
Amitosis,  57,  64 
Amphiaster,  62 

Amphibia,  epithelium  of  alveoli  of,  281 
Amphophile  granules,  technic,  205 
Ampullae  of  Thoma,  182 
Anaphases,  57,  63 
Anastomoses  of  vessels,  199 
Anilin  stains,  42 
Annulospiral  nerve-ending,  162 
Annulus  fibrosus,  436 

atrioventricularis,  191 
Anterior  elastic  membrane  of  cornea,  410 

endothelium  of  iris,  416 

epithelium  of  crystalline  lens,  428 

ground  bundle,  370 

lymph-channels  of  eye,  429 
Anterolateral  columns,  ascending,  370 

descending,  370 

Antrum  of  Graafian  follicle,  309 
Anus,  249 
Apathy's  method  for  demonstration  of  fibril- 

lar  elements  of  nervous  system,  404 


Apicis  dentis,  foramen,  213 
Apochromatic  lens,  19 
Aponeuroses,  96 
Aqueous  humor,  407 
Arachnoid,  394 
Arches  of  Corti,  448 
Arcuate  fibers  of  cornea,  411 
Area  cribrosa,  295 

of  Langerhans,  pancreatic,  267 

vasculosa,  1 68 
Arrectores  pilorum,  354 
Arteriae  arci  formes,  296 

capsulares  glomeruliferae,  297 
Arterial  circle  of  Zinn,  426 

trunks,  great,  194 
Arteries,  194 

intralobular,  296 

medium- sized,  195 

precapillary,  196 
Arteriolae  rectae  spuriae,  296 

rectae  verae,  297 

Ascending  anterolateral  columns,  370 
Atresia  of  ovarian  follicles,  315 
Attraction-sphere,  55 
Auditory  artery,  internal,  452 

canal,  external,  435,  436 

cells,  outer,  449 

hairs,  448 

nerve,  452 

organ,  435.     See  also  Ear. 

ossicles,  438 

teeth,  446 

Auerbach's  plexus,  254 
Auriculoventricular  valves,  191 
Axial  canals  of  small  intestines,  253 

cords,  142 

sheath    of    neuromuscular    nerve    end- 
organs,   1 60 

thread  of  spermatosome,  323 

sheath  of,  323 
Axis-cylinder  of  nerve-fibers,  144 

processes,  134 
Axis-fibrils,  142 
Axolemma,  142 
Axones,  134 


BAILLARGER'S  striation,  379 
Bars  of  intercellular  cement,  80 
Bartholin's  glands,  322 
Basement  membranes,  75 


INDEX. 


Basement  membranes  of  small  intestine,  246 
Basic  stains,  40 
Basichromatin  granules,  56 
Basilar  membrane,  444,  447 
Basket  cells  of  salivary  glands,  228 
Basophile  granules,  174 

technic  of,  206 

Bechtereff  and  Kaes's  striation,  379 
Benda'  s  method  for  demonstration  of  med- 
ullary sheath,  399 
Berkley' s  method  for  demonstrating  nerves 

of  liver,  274 

Berlin  blue  as  injection  fluid,  49 
Bertini's  columns,  289 
Bethe's  method  for  staining  neurofibrils  and 

Golgi-nets,  405 
Bile  capillary,  258,  259 
Bile-ducts,  263 
Bismarck  brown,  43 
Bladder,  300 
Blastema,  56 
Blastomeres,  64,  73 
Blood,  168 

current,  demonstration  of,  through  ves- 
sels, 208 

formation  of,  168 
islands,  168 
plasma,  169,  176 
platelets,  176 
shadows,  170 
sinus,  199 
technic  of,  203 
Blood-cell,  behavior  of,  in  blood  current, 

177 
red,  nucleated,  containing  hemoglobin, 

1 86 
Blood-corpuscles,  red,  169 

white,  173 
Blood-forming  organs,  168 

technic  of,  202 
Blood-vessels,  168,  193 
Bohmer's  hematoxylin,  41 
Bone,  103 

breakers,  in.     See  also  Osteoclasts. 
canaliculi,  103,  104 
compact,  of  shaft,  development  of,  115 
corpuscles,  104 

isolation  of,  123 
development  of,  107 
endochondral,  107 
intracartilaginous,  107 
intramembranous,  107,  113 

development  of,  113 
lacunae  of,  103,  104 
lamellae  of,  104 
large,  examination  of  denser  structure  of, 

121 

spaces  in,  Ranvier's  method  to  demon- 
strate, 121 
structure  of,  103 
Bone-cells,  103 
Bone-marrow,  185 
blood-vessels  in,  188 
red,  185 
technic  of,  209 
yellow,  185,  188 


Bony  cochlea,  443 

labyrinth,  439 
Borax-carmin,  alcoholic,  as  stain,  40 

aqueous,  as  stain,  40 
Bottcher's  cells,  450 
Boundary  zone,  choroid,  413 
Bowman's  capsule,  287 

glands,  457 

membrane,  410 
Brain-sand,  381 
Bronchi,  277 

branches  of,  277 
Bronchioles,  277 

respiratory,  279 
Brownian  movement,  53 
Bruch's  membrane,  416 
Brunner's  glands,  236,  246 
Budding,  56 
Bulb  hairs,  354 
Bulbus  oculi,  407 
Bundles,  tendon,  primary,  96 

secondary,  97 
Burdach's  column,  370 


cupolare,  444 

vestibulare,  444 
Camera  lucida,  20 

Canada  balsam  as  mounting  medium,  46 
Canaliculi,  bone,  103,  104 
Canalis  communis,  labyrinth  of,  440 
Capillaries,  198 

bile,  258,  259 

lymph,  201 
Capsule,  cartilage,  loo 

of  glands,  84 

of  Glisson,  257 

of  lymph-gland,  178 

of  Tenon,  409 

Carbol-xylol  as  clearing  fluid,  47 
Carbon  dioxid,  cutting  tissues  frozen  with, 

35,  36 

Cardiac  muscle-cells,  132 
Carmin  as  stain,  40 
Carmin-bleu  de  lyon  of  Rose,  44 
Carotid  gland,  202 
Cartilage,  99 

capsule,  100 

cell,  99 

embryonal,  99 

fibro- elastic,  102 

ground -substance  of,  99 

hyaline,  99 

lacunae  of,  100 

matrix  of,  99 

nutrition  of,  IO2 
Cecum,  249 
Cell,  51 

auditory,  449 

basket,  of  salivary  glands,  228 

blood-,  behavior  of,  in  blood  current,  177 

bone-,  103 

Bottcher's,  450 

Brownian  movement  of,  53 

cartilage,  99 

centro-acinal,  266 


INDEX. 


485 


Cell,  chief,  of  acini  of  thyroid  body,  284 

of  hypophysis,  381 

of  stomach,  239 

peptic,  239 

chromophilic,  of  hypophysis,  381 
ciliated,  cylindric,  53 
colloid,  of  acini  of  thyroid  body,  284 
cone-visual,  419 
connective-tissue,  fixed,  94 
containing  pigment,  184 
cortical,  small,  of  cerebellar  cortex,  374 
Deiters's,  449 
delomorphous,  238 
demonstration  of  granules  in,  71 
Altmann's  method,  72 

of  structure  of,  68 
diagram  of,  52 
diffuse,  of  retina,  425 
double  staining  of,  69 
endothelial,  74,  86 

demonstration  of,  88 
eosinophile,  187 

transitional,  187 
ependymal,  392 

epithelial,  isolated,  examination  of,  87 
fat-,  scheme  of,  99 
fixing  of,  69 

chromic  acid  for,  69 

corrosive  sublimate  for,  69 

Flemming's  solution  for,  69 

picric  acid  for,  69 
flagellate,  53 
follicular,  334 

ganglion,  134.     See  also  Ganglion  cell. 
germinal,  85 

giant,  of  bone-marrow,  187 
gland-,  8l 
glandular,  54,  239 

adelomorphous,  239 

central,  239 

chief,  239 

peptic,  239 
goblet,  8 1 
granular,  95 

of  cerebellar  cortex,  375 
hair-,  auditory,  448,  449 

of  utriculus,  442 
Hensen's,  449,  450 
hepatic,  cords  of,  258 
lutein,  314 
marrow,  186 
mesameboid,  74 
migratory,  94,  96,  175 
molecular  movement  of,  53 
monostratified,  of  retina,  425 
muscle-,  123.     See  also  Muscle-cell. 
nerve-,  134.     See  also  Ganglion  cell. 
neuro-epithelial,  85 
neurogliar,  393 
of  Claudius,  450 
of  Golgi  of  cerebral  cortex,  377 
of  Kupffer,  262 
of  Langerhans,  266 
of  Leydig,  431 

of  Martinotti  of  cerebral  cortex,  377 
of  Purkinje  of  cerebellar  cortex,  374 


Cell  of  Sertoli.  326 
olfactory,  456 
oxyntic,  238 
parietal,  238 
pigment,  71,  95,  96 
pillar,  of  organ  of  Corti,  448 

heads  of,  448 
plasma,  96 
polarity  of,  75 

polygonal,  of  cerebral  cortex,  376 
polymorphous,  of  cerebral  cortex,  377 
polynuclear,  64 
polystratified,  of  retina,  425 
Purkinje's,  138 

pyramidal,  large,  of  cerebral  cortex,  376 
of  cerebral  cortex,  138 
small,  of  cerebral  cortex,  376 
rod-visual,  418 
segmentation,  64 
seminal,  primitive,  334 
sense,  75 

sexual,  matured,  65 
somatic,  65 
spider-,  393 

spindle,  of  cerebral  cortex,  376 
staining  of,  69 

stellate,  of  cerebellar  cortex,  374 
of  cerebral  cortex,  376 
of  liver,  262 
sustentacular,  85,  334 
technic  of,  68 
tegmental,  224 

triangular,  of  cerebral  cortex,  376 
visual,  418 

wandering,  53,  94,  96 
with  eosinophile  granules,  187 
Cell -body,  52 
of  neurones,   134.     See  also  Ganglion 

cell. 

Cell-division,  56 
direct,  57,  64 
indirect,  57 
mitotic,  diagrammatic,  58 

of  fertilized  whitefish  eggs,  60 
Cell-microsomes,  52 
Celloidin  imbedding,  28 

diagram  for,  29 
infiltration,  28 

diagram  for,  29 

sections,  cutting  of,  with  sliding  micro- 
tome, 33 

fixation  of,  to  slide,  39 
Celloidin-pararfin  imbedding,  29 

infiltration,  29 
Cell-plate,  64 
Cell-spaces,  94 
Cementum,  215,  220 
Central  artery  of  retina,  426 
nervous  system,  365 

blood-vessels  of,  397 
membranes  of,  393 
technic  of,  397 
spindle,  62 
vein  of  liver  lobule,  258 

of  retina,  426 
Centro-acinal  cells,  266 


486 


INDEX. 


Centrosome,  55 
Centrosphere,  55 
Cerebellar  columns,  direct,  370 
cortex,  372 

granular  layer  of,  375 
medullary  substance  of,  375 
molecular  layer  of,  372 
Cerebral  cortex,  375 

cells  of  Golgi  of,  377 
cells  of  Martinotti  of,  377 
layer  of  large  pyramidal  cells,  376 
of  polymorphous  cells,  377 
of  small  pyramidal  cells,  376 
medullary  substance  of,  378 
molecular  layer  of,  376 
Ceruminous  glands,  357,  436 
Chemotaxis,  54 
Chemotropism,  54 

Chief  cells  of  acini  of  thyroid  body,  284 
of  hypophysis,  381 
of  stomach,  239 
Chondrin,  103 
Choroid,  407,  412 
arteries  of,  416 
layers  of,  412 
plexus,  396 
Choroidal  fissure,  408 
Chromatin,  55 
Chromatolysis,  68 

technic  of,  68 
Chromatophile  granules  of  ganglion  cell, 

134. 

Chromic  acid  as  fixing  solution,  24 

for  cells,  69 

Chromophilic  cells  of  hypophysis,  381 
Chromosomes,  61 

daughter,  62 

Chrzonszczewsky' s  physiologic  auto-injec- 
tion, 272 

Chyle-vessels,  253 
Cilia,  75 

movement  of,  87 

of  eyelids,  430 
Ciliary  body,  407,  412,  414 
nerve  supply  of,  417 

glands,  414 
of  Moll,  430 

muscle,  414 

processes,  414 
Ciliated  cell,  53 
Circulatory  system,  190 

technic  of,  210 
Circulus  arteriosus  iridis  major,  416 

minor,  416 

Circumanal  glands,  250,  357 
Circumvallate  papilloe,  223,  225 
Clarke's  column,  367 
Claudius'  cells,  450 
Clitoris,  322 
Cloquet's  canal,  429 
Coal-tar  stains,  42 
Cochlea,  443 

bony,  443 

perilymph  of,  454 

spiral  ganglion  of,  452 
Cochlear  duct,  443,  444 


Cohnheim's  fields,  127 

method  for  demonstrating  nerve -fibers, 

1 66 

Coil-glands  of  skin,  357 
Collective  lens,  19 
Colloid  cells  of  acini  of  thyroid  body,  284 

material,  284 
Colostrum,  362 

corpuscles,  362 

Columnae  rectales  Morgagni,  250 
Columns  of  Bertini,  289 

of  Burdach,  370 

of  Clarke,  367 

of  Goll,  370 

of  Tiirck,  370 
Commissures,  371 
Compound  microscope,  17 
Concretions,  prostatic,  332 
Condensers,  19 
Cone-fibers  of  retina,  419 
Cone- visual  cells,  419 
Coni  vasculosi  Halleri,  326 
Conjunctiva,  430 

scleral,  409 
Connective  tissue,   89.     See  also  Tissue^ 

connective. 

Connective-tissue  cells,  fixed,  94 
Conus  medullaris,  365 
Convoluted  tubules,  325,  327 
Corium,  341,  344.     See  also  Dennis. 
Cornea,  407,  410 

nerves  of,  412 

technic  of,  434 
Corneal  corpuscles,  411 

spaces,  411 

technic  of,  434 
Corona  radiata,  309 
Corpora  amylacea,  332 
Corpus  albicans,  315 

Highmori,  325 

luteum,  313 
Corpuscles,  connective-tissue,  94 

blood-,  red,  169 
white,  173 

bone,  104 

isolation  of,  123 

colostrum,  362 

corneal,  411 

genital,  155 

Golgi-Mazzoni,  350 

Hassall's,  189,  190 

Malpighian,  180,  182,  287,  289 

Meissner's,  155 
technic  of,  364 

of  Grandry,  350 
technic  of,  364 

of  Herbst,  158,  350 
technic  of,  364 

Pacinian,  157 

technic  of,  364 

Corrosive  sublimate  as  fixing  fluid  for  car- 
tilage, 120 
as  fixing  solution,  23 
for  fixing  cells,  69 
Cortical  cells,  small,  of  cerebellar  cortex, 

374 


INDEX. 


487 


Cortical  layer  of  hair,  35 1 

nodules  of  lymph-glands,  179 

substance  of  kidney,  288 
Corti's  arches,  448 

organ,  447 
cells  of,  447 
characteristics  of,  450 

tunnel,  448 
Cover-slip,  20 
Cowper's  glands,  332 
Cox's  method  for  demonstration  of  ganglia 

cells,  401 

Crescents  of  Gianuzzi,  229 
Crista  basilaris,  446 
Cristae,  440,  441 
Crossed  pyramidal  columns,  370 
Crosses  of  Ranvier,  164,  165 
Crystalline  lens,  428 
Cupola,  443 

Currents  of  diffusion,  27 
Cuticle,  341.     See  also  Epidermis. 

of  hair,  351 
Cuticula,  54,  75 

dentis,  213 
Cuticular  membrane,  75 

ridge,  436 

structures,  75 
Cutis,  341 
Cytoplasm,  52 
Cytolymph,  53 
Czocor's  cochineal  solution,  41 


DAMAR  as  mounting  medium,  47 
Daughter  chromosomes,  62 

stars,  336 
Decalcification,  122 

v.  Ebner's  method,  122 
Decalcifying  fluids,  122 
hydrochloric  acid,  122 
nitric  acid  solution,  122 
Deiters's  cells,  449 

processes,  134 
Delafield's  hematoxylin,  41 
Delomorphous  cells,  238 
Demilunes  of  Heidenhain,  229 
Dendrites,  134,  135 

of  sensory  neurones,  216 
Dendritic  fibrous  structures  of  Gruber,  437 
Dental  sac,  218 
Dentin,  214,  218 
Dentinal  bulbs,  217 

fibers,  215,  216,  218 

papillae,  217 

tubules,  214 
Dermis,  341 

lymph-vessels  of,  348 
Descemet's  membrane,  411 
Descending  anterolateral  columns,  370 
Deutoplastic  granules,  311 
Diapedesis,   175,  201 
Diaster,  63,  336 
Diffuse  cells  of  retina,  425 

spongioblasts,  424 
Diffusion,  current  of,  27 
Digestive  organs,  210 


Digestive  organs,  technic  of,  269 
Dilator  muscle  of  pupil,  416 
Direct  cell-division,  57,  64 

cerebellar  columns,  370 

pyramidal  tract,  370 
Discus  proligerus,  309 
Dispirem,  63 
Double  knife,  21 

staining,  43 

of  cells,  69 

Doyere's  elevation,  147 
Ductus  endolymphaticus,  440,  454 
Dura  mater,  393 


EAR,  435 

external,  435 

internal,  439 

middle,  437 

technic  of,  455 

vestibule  of,  439 
Ectoderm,  51,  73 

tissues  derived  from,  73 
Egg  tubes,  primary,  of  Pfliiger,  307 
Ehrlich-Biondi  triple  stain,  45 
Ehrlich's  hematoxylin,  42 

leucocytic  granules,  174 

methylene-blue  method  for  ganglion  cells 
and  nerve-fibers,  402 

neutrophile  mixture,  206 
Ejaculatory  ducts,  330 
Elastic  fibers,  91 

fibrous  tissue,  98 

membrane,  anterior,  of  cornea,  410 

posterior,  of  cornea,  41 1 
Eleidin,  343 
Embryonal  cartilage,  99 
Enamel,  213 

germs,  217 

prisms,   213 

Encoche  d' ossification,  112 
End-brush,  147,  151 
End-bulb  of  Krause,  154 

cylindric,  157 
Endocardium,  190 

Endolymph  of  membranous  labyrinth,  453 
Endomysium,  129 
Endoneurium,  145 
Endoplasm,  188 

End-organs,  nerve,  neuromuscular,  158. 
See  also  Nerve  end-organs,  neuro- 
muscular. 

neurotendinous,  162 
Endosteum,   185 

Endothelial  and  mesothelial  cells,  relations 
of,  87 

cells,  74,  86 

demonstration  of,  88 
Endothelium,  85 

anterior,  of  iris,  416 
End-piece  of  Retzius,  323 
Engelmann's  accessory  disc,  127 
Entoderm,  51,  73 

tissues  derived  from,  74 
Eosinophile  cell,  187.     See  also  Cell,  eosin- 

ophile* 


488 


INDEX. 


Eosinophile  granules,  174.    See  also  Gran- 
ules, eosinophile. 
Ependymal  cells,  392 
Epicardium,  191 
Epidermis,  341 

compensation  for  desquamation  of,  344 

layers  of,  341 

nerves  of,  technic  of,  364 

pigment  in,  346 

technic  of,  362- 
Epidural  space,  394 
Epilamellar  plexus,  232,  358 
Epimysium,  129 
Epiphysis,  380 
Epithelial  cells,  isolated,  examination  of,  87 

tissue,  74 

technic  of,  87 

Epithelium,  anterior,    of   crystalline   lens, 
428 

ciliated,  islands  of,  in  cervical  canal,  318 

columnar,  pseudostratified,  77 
simple,  77 

examination  of,  87 

germinal,  of  ovary,  307 

glandular,  8 1 

neuro-,  85 

of  urethra,  333 

posterior,  of  iris,  416 

respiratory,  280 

simple,  76 
cubic,  76 
squamous,  76 

stratified,  77 
columnar,  79 
squamous,  78 

technic  of,  87 

transitional,  79 
Eponychium,  356 
Epoophoron,  322 
Erlicki's  fluid,  25 
Erythroblasts,  186 
Erythrocytes,  169 
Esophagus,  233 

technic  for,  271 
Eustachian  tube,  438,  439 
Excretory  duct  of  testis,  329 

ducts,  membrane  of,  82 
Exoplasm,  188 
External  auditory  canal,  435,  436 

limiting  membrane  of  retina,  420,  422 
Eye,  407 

anterior  lymph-channels  of,  429 

development  of,  407 

fetal  blood-vessels  of,  429 
'general  structure  of,  407 

pigment  layer  of,  418 

protective  organs  of,  430 

technic  for,  433 

tunics  of,  407 
Eyeball,  407 

interchange  of  fluids  in,  429 
Eyelids,  430 

conjunctival  portion  of,  430 

cuticular  portion  of,  430 

middle  layer  of,  432 

"third,"  432. 


FALLOPIAN  tubes,  316 
nerve-supply  of,  320 
technic  for,  340 
Farrant's  gum  glycerin,  48 
Fasciculus  gracilis,  370 
Fat,  absorption  of,  by  intestine,  256 

lobules,  99 

Fat-cell,  scheme  of,  99 
Fat-marrow,  185, 1 88 
Female  genital  organs,  306 

pronucleus,  67 
Fenestra  cochleae,  438 

rotunda,  438 

Fenestrated  membranes,  98 
Ferrein's  pyramids,  289 
Fertilization,  diagram  of,  66 

process  of,  65 

Fetal  blood-vessels  of  eye,  429 
Fiber,  cone-,  of  retina,  419 
dentinal,  215 
elastic,  91 

intrafusal,  of  neuromuscular  nerve  end- 
organs,  159 

Kupffer's  reticular,  185 
lens,  428 

Muller's,  of  retina,  422 
muscle-,  striped,  124 
nerve-,  142.     See  also  Nerve-fiber. 
Purkinje's,  190 

muscle-cells  of,  132 
Remak's,  145 
rod-,  of  retina,  419 
Sharpey's,  106 

sustentacular,  of  Deiters's  cells,  450 
tunnel-,  452 

white,  of  connective  tissue,  90 
Fiber-baskets  of  retina,  423 
Fibrae  circulares,  415 
Fibrillar  mass  of  Flemming,  53 
Fibrils  of  axial  cord,  demonstration  of,  165 
Fibrin,  176,  207 

demonstration  of,  208 
Fibrocartilage,  white,  102 
Fibro-elastic  cartilage,  IO2 
Filiform  papillae,  222 
Filum  terminale,  365 
Fimbriae  linguae,  223 
Fixation  to  slide,  of  sections,  38 
Fixing  methods,  22 
solutions,  22 

acetic  sublimate,  24 
alcohol,  22 
chromic  acid,  24 
corrosive  sublimate,  23 

for  cartilage,  I2O 
Erlicki's,  25 
Flemming' s,  22 
Fol's,  23 
.     formalin,  25 
formol,  25 
Hayem's,  203 
Hermann's,  23 
Muller's,  24 
nitric  acid,  24 
osmic  acid,  22 

for  cartilage,  I2O 


INDEX. 


Fixing  solutions,  picric  acid,  23 

picric-nitric  acid,  23 

picric-osmic-acetic  acid,  24 

picric -sublimate-osmic  acid,  24 

picrosulphuric  acid,  23 

Rabl's,  24 

Zenker's,  25 
Flagellate  cell,  53 
Flagellum  of  spermatosome,  323 
Flemming's  fibrillar  mass,  53 
interfibrillar  substance,  53 
solution,  22 

for  fixing  cells,  69 
Flower-like  nerve-ending,  162 
Fluids  in  eyeball,  interchange  of,  429 
Foam-structures,  73 
Foliate  papillae,  223 
Follicles,  simple,  of  adenoid  tissue,  177 
Follicular  cells,  334 
Folliculi  linguales,  225 
Fol's  solution,  23 
Fovea  centralis,  421 
Fontana's  spaces,  415 
Foramen  apicis  dentis,  213 
Foramina  nervosa,  446 

papillaria,  293 

Formalin  as  fixing  solution,  25 
Formol  as  fixing  solution,  25 
Fragmentation,  direct,  65 
Free-hand  sectioning,  21 
Freezing  apparatus  for  sliding  microtome, 

35 

Friedlander's  glycerin-hematoxylin,  42 
Front  lens,  19 

Fundus  of  fovea  centralis,  421 
Fungiform  papillae,  222 
Funiculi  of  nerve-trunk,  145 
compound,  147 


GANGLIA,  382 
spinal,  382 
sympathetic,  385 
Ganglion  cell,  134 

bipolar,  135,  137 

chromatophile  granules  of,  134 

demonstration  of,  1 66 

layer  of  retina,  420,  425 

multipolar,  137 

of  Dogiel,  in  spinal  ganglia,  384 

sympathetic,  140 

technic  of,  399 

unipolar,  137 
spiral,  of  cochlea,  452 
Gartner's  duct,  322 
Gastric  crypts,  237 
glands,  237 

body  of,  238 

fundus  of,  238 

neck  of,  238 
Gastrulation,  73 

Gelatin-carmin  as  injection  fluid,  48 
Gelatinous  substance  of  Rolando,  367 
Genital  corpuscles,  155 
organs,  female,  306 


Genital  organs,  male,  323 
Genito-urinary  organs,  287 
Germ   centers  of    lymphoid  tissue,    175, 
178 

layers,  51 
Germinal  cells,  85 

epithelium  of  ovary,  307 

spot,  56 

vesicle,  65 
Germs,  enamel,  217 
Giant-cells,  64,  187 
Gianuzzi's  crescents,  229 
Giraldes,  organ  of,  329 
Gland-cell,  81 
Glands,  alveolar,  84 

Brunner's,  236,  246 

capsule  of,  84 

carotid,  202 

ceruminous,  357,  436 

ciliary,  414 
Moll's,  430 

circumanal,  250,  357 

classification  of,  82 

coil-,  of  skin,  357 

gastric,  237.     See  also  Gastric  glands. 

lacrimal,  432 

lenticular,  241 

Lieberkuhn'  s,  245 

lymph-,    177,    178.     See   also  Lymph- 
glands. 

mammary,    359.     See    also  Mammary 
glands. 

mixed,  230 

mucous,  228 

multicellular,  82 

of  Bartholin,  322 

of  Bowman,  457 

of  Cowper,  332 

of  Littre,  333 

of  Moll,  357 

of  Montgomery,  361 

of  mouth,  small,  231 

of  oral  cavity,  227 

of  skin,    357.     See   also   Skin,  glands 

°f- 

of  Tyson,  334 
parotid,  228 
pineal,  350 
saccular,  84 

salivary,  228.     See  also  Salivary  glands. 
sebaceous,  358 
serous,  228 
structure  of,  82 
sublingual,  228 
submaxillary,  230 
sudoriparous,  357 
suprarenal,  301.     See   also  Suprarenal 

glands. 
sweat-,  357 
thymus,  188 
thyroid,  284 
tubular,  82 

branched,  83 

compound,  83 

reticulated,  83 
Glandula  carotica,  202 


490 


INDEX. 


Glandulse  buccales,  211 
duodenales,  236 
labiales,  21 1 
Glandular  cells,  54,  239.     See  also  Cell, 

glandular. 
epithelium,  81 
Glassy  layer  of  choroid,  412,  414 

membrane,  352 

Glia  covering  of  pia  mater,  396 
Glisson's  capsule,  257 
Glomeruli  arteriosi  cochleae,  453 
Glomerulus,  287 
Glomus  caroticum,  202 
Glossary  of  literature,  460 
Glycerin,  Farrant's  gum,  48 

mounting  in,  47 

Glycerin-albumen  for  fixing  paraffin  sec- 
tions to  slide,  38 
Goblet  cells,  81 

Gold  chlorid  as  stain  for  capsules  of  car- 
tilage, 120 

Golgi-Mazzoni  corpuscle,  350 
Golgi's  cell  of  cerebral  cortex,  377 

methods  for  demonstration  of  ganglion 

cells,  399 
mixed,  401 
rapid,  401 
slow,  400 
preparations,     methods    of    mounting, 

402 

tendon  spindle,  162 
GolPs  column,  370 
Gowers's  columns,  370 
Graafian  follicle,  309 
antrum  of,  309 
bursting  of,  313 
Grandry' s  corpuscles,  350 

technic  for,  364 
Granular  cells,  95 

of  cerebellar  cortex,  375 
layer,  Tomes',  220 
sole  plate,  148 

Granules,  acidophile,  technic  for,  205 
amphophile,  technic  for,  205 
basophile,  174 

technic  for,  206 
demonstration  of,  in  cells,  71 
deutoplastic,  311 
eosinophile,  174 
cells  with,  187 
technic  for,  205 
interstitial,  of  Kolliker,  129 
leucocytic,  Ehrlich's,  174 
mast-cell,  technic  for,  205 
neutrophile,  174 

technic  for,  206 
yolk,  311 
Gray  matter,  136 

substance  of  spinal  cord,  365 
Ground  bundle,  anterior,  370 

plexus  of  cornea,  412 
Ground-substance,  interfascicular,  97 
of  areolar  connective  tissue,  93 
of  cartilage,  99 

Gruber'  s  dendritic  fibrous  structures,  437 
Gustatory  organs,  223 


HAIR,  350 

auditory,  448 

bulb,  351,  354 

cells  of  utriculus,  442 

cortical  layer  of,  35 1 

cuticle  of,  35 1 

follicle,  351 

nerve-fibers  of,  354 

germ,  351 

glassy  membrane  of,  352 

growth  of,  353 

medullary  substance  of,  351 

olfactory,  457 

papilla,  351 

root,  351 

root-sheaths  of,  351 
inner,  351 
outer,  351 

shaft,  351 

shedding  of,  354 

technic  for,  364 
Hamulus,  444 

Hassall's  corpuscles,  189,  190 
Haversian  canals,  103 

spaces,  in 
Hayem's  solution,  203 
Hearing,  organ  of,  435 

technic  for,  455 
Heart,  168,  190 

coats  of,  190 

elastic  tissue  of,  distribution  in,  191 

muscle-cell,   149 

nerve  supply  of,  192 
Heidenhain's  demilunes,  229 

iron-lack  hematoxylin,  42 
Helicotrema,  444 
Heliotropism,  54 
Heller's  plexus,  251 
Hemalum  as  stain,  42 
Hematin,  169 

Hematoidin,  demonstration  of,  207 
Hematoxylin  as  stain,  41.    See  also  Stains. 

Delafield'  s,  for  demonstrating  canalicular 

system  in  cartilage,  120 
Hematoxylin-eosin  as  stain,  44 
Hematoxylin-safranin  of  Rabl  as  stain,  44 
Hemin,  169 

isolation  of,  207 
Hemoglobin,  169 

demonstration  of,  206 
Hemokonia,  176 
Henle's  layer,  351 

loop,  288,  291 

ascending  limb  of,  288,  291 
descending  limb  of,  288,  291 

sheath,  147 
Hensen's  cells,  449,  450 

median  disc,  127 
Hepatic  cells,  cords  of,  258 

cords,  258 
Herbst's  corpuscles,  158,  350 

technic  for,  364 
Hermann's  solution,  23 
Heterotypic  form  of  mitosis,  64 
Highmore,  body  of,  325 
Hilum  of  lymph-gland,  178 


INDEX. 


491 


Histology,  genera],  51 
special,  1 68 

Homeotypic  mitosis,  64 

Honing  microtome  knife,  36  - 

Horn-sheath  of  nerve-fibers,  142 

Howship's  lacume,   in 

Huber's  method  for  mounting  Golgi's  pre- 
parations, 402 

Huschke's  auditory  teeth,  446 

Huxley's  layer,  351 

Hyaline  cartilage,  99 

Hyaloid  arteries,  posterior,  429 
canal,  429 
membrane,  427 

Hyaloplasm,  53 

Hydatids  of  Morgagni,  322 

Hydrochloric    acid   as   decalcifying   fluid, 

122 

Hydrotropism,  54 
Hymen,  321 

Hypolamellar  plexus,  232 
Hypophysis,  381 


IMBEDDING,  25 

celloidin,  28.     See  also  Celloidin  imbed- 
ding. 

celloidin-paraffin,  29 
paraffin,  26.     See  also  Paraffin  imbed- 
ding. 

tissues,  box  for,  26 
Immersion  lens,  19 
Implantation  cone,  135 
Indifferent  fluids,  21 
Kronecker's,  21 
physiologic  saline  solution,  21 
Ranvier's  iodin  and  potassium  iodid, 

21 

Ripart  and  Petit' s,  21 
Schultze's  iodized  serum,  21 
Indirect  cell-division,  57 
Inferior  nasal  artery  of  retina,  427 

vein,  427 
papillary  artery,  426 

vein,  426 
Infiltration,  25 

celloidin,  28.     See  also  Celloidin  infil- 
tration. 

celloidin-paraffin,  29 
paraffin,  26.     See  also  Paraffin  infiltra- 
tion. 

Infundibula,  279 
Injection  fluids,  48 
Berlin  blue,  49 
gelatin-carmin,  48 
methods  of,  introduction  to,  48 
of  lymph-channels,  49 
of  lymph-spaces,  49 
of  lymph-vessels,  49 
Inner  molecular  layer  of  retina,  420,  423 

nuclear  layer  of  retina,  420,  423 
Intercellular  bridges,  75,  342 

demonstration  of,  88 
spaces,  75 
substance,  73 
Interfascicular  ground- substance,  97 


Interfibrillar  substance  of  Flemming,  53 
Interglobular  spaces,  215 
Interlobular  duct  of  pancreas,  266 
Intermediate  disc  of  Krause,  127 

tubule  of  pancreas,  266 
Internal  auditory  artery,  452 

limiting  membrane,  422 
Interpapillary  epithelial  processes,  79 
Interstitial  granules  of  Kolliker,  129 
Intertubular  cell-masses  of  pancreas,  267 
Intestine,  235 

absorption  of  fat  by,  256 

blood  supply,  251 

large,  249 

lymph  supply  of,  251 

mucous  membrane  of,  structure  of,  235 

nerve  supply  of,  251 

secretion  of,  256 

small,  243 

axial  canals  of,  253 
crypt  of,  248 
lacuna  of,  248 
technic  for,  271 
Intracapsular  plexuses,  387 
Intralobular  arteries  of  kidney,  296 

vein,  258,  261,  298 

lodo-iodid  of  potassium  stain  to  demon- 
strate glycogen  in  cartilage,  121 
Iris,  407,  412,  415 

diaphragm,  18 

layers  of,  415,  416 

nerve  supply  of,  417 
Islands  of  ciliated  epithelium  in  cervical 

canal,  318 
Isolating  fluids,  87 


JAPANESE  method  for  fixing  paraffin  sec- 
tions to  slide,  39 
Jung's  sliding  microtome,  33,  34 


KARYOKINESIS,  57 

Karyokinetic  cell-division,  heterotypic,  336 

homeotypic,  336 
Karyolymph,  55 
Karyolysis,  68 

technic  of,  68 
Keratohyalin,  342 

technic  for,  362 
Kidney,  287 

arched  collecting  portion  of  tubules,  288, 

293 

blood-vessels  of,  295 
cortical  substance  of,  288 
distal  convoluted  portion  of  tubules,  288, 

292 

intercalated  portion  of  tubules,  288,  292 
medullary  substance  of,  288 
pelvis  of,  300 
proximal  convoluted  portion  of  tubules, 

288,  290 

straight  collecting  tubules  of,  288 
Knife,  double,  21 
Kolliker' s  interstitial  granules,  129 
muscle  columns,  126 


492 


INDEX. 


Kopsch's  technic  for  ganglion  cells,  402 
Krause's  end-bulb,  154 
cylindric,  157 

intermediate  disc,  127 

transverse  membrane,  127 
Kronecker's  fluid,  21 
Kronig'  s  varnish,  48 
Kupffer's  method  of  treating  liver  tissue, 

273 

reticular  fibers,  185 
Kytoblastema,  56 


LABIUM  tympanicum,  446 

vestibulare,  445 
Labyrinth,  bony,  439 

development  of,  454 

membranous,  439,  440 

osseous,  439 
Lacrimal  apparatus,  432 

gland,  432 

sac,  433 

Lacteals  of  villi,  253 
Lacuna  of  small  intestine,  248 
Lacunae,  Howship's,  III 

of  bone,  103,  104 

of  cartilage,  100 
Lagena,  444 
Lamellae,  97 

marrow,  104 

of  bone,  104 

periosteal,  104 
Lamina  basil aris  propria,  447 

choriocapillaris,  413 

cribrosa,  409,  425 

elastica  interna,  195 

fusca,  409 

propria  of  oral  cavity,  21 1 

reticularis,  447,  451 

spiralis  membranacea,  444,  447 
ossea,  444,  445 

suprachoroidea,  412 

vasculosa  Halleri,  413 
Langerhans,  areas  of,  267 

cells  of,  266 
Lanthanin,  56 
Large  intestine,  249 
Larynx,  275 
Lateral  column,  367 

mixed,  370 
Layer  of  Henle,  351 

of  Huxley,  351 
Leucocytes,  173,  187 

polynuclear,  amitotic  division  of,  64 
Lens,  407 

apochromatic,  19 

capsule,  428 

collective,  19 

crystalline,  428 

fibers,  428 

front,  19 

immersion,  19 

ocular,  19 

suspensory  ligament  of,  428 

technic  of,  434 
Lenticular  glands,  241 


Leydig's  cells,  431 
Lieberkiihn's  crypts,  245 

glands,  245 
Ligaments,  96 
Ligamentum  pectinatum  iridis,  415 

spirale,  444,  446 
Limbus  spiralis,  445 
Limiting  membrane,  external,  420,  422 

internal,  422 

Lingual  mucous  membrane,  221 
papillae  of,  221 

papillae,  221 
Linin,  55 

Liquor  folliculi,  309 
Literature,  glossary  of,  460 
Littre's  glands,  333 
Liver,  257 

development  of,  265 

lobules,  257 

lymph-vessels  of,  263 

nerves  of,  264 
technic  of,  274 

technic  of,  272 

Kupffer'  s  method,  273 

vascular  system  of,  260 
Lobes,  renal,  287 
Lobules,  fat,  99 

liver,  257 

spleen,  182 
Loop  of  Henle,  288,  291.  See  also 

Henle*  s  loop. 

Lowit's  method   of  demonstrating  nerve- 
fibers,  167 
Lung,  blood-vessels  of,  281 

lymphatics  of,  282 

tissue,  281 
Lunula,  356 
Lutein  cells,  314 
Lymph,  168 

canalicular  system,  94 

capillaries,  201 

Lymphatic  glands,  capsule  of,  178 
technic  for,  208 

system,  200 
Lymph-channels,  anterior,  of  eye,  429 

injection  of,  49 
Lymph-follicles  of  tongue,  225 

of  tonsils,  225 

solitary,  177 

Lymph-glands,  177,  178 
Lymph-nodules,  177 

agminated,  177 
Lymphocytes,  173,  175,  187 
Lymphoid  tissue,  177 
Lymph-sinus,  179 
Lymph-spaces,  2OI 

injection  of,  49 

periaxial,   of  neuromuscular  end-organ, 
160 

perichoroidal,  413 
Lymph-vessels,  168,  200 

injection  of,  49 

MACERATING  fluids,  87 
Macula  acustica  sacculi,  441 
utriculi,  441 


INDEX. 


493 


Macula  lutea,  421 
region  of,  421 
Magenta  red  as  stain  for  connective  tissue, 

119 
Male  genital  organs,  323 

pronucleus,  67 
Malpighian  bodies,  180,  182 
corpuscles,  180,  182,  287,  289 
layer,  technic  of,  363 
Mammary  glands,  359 

human,  structure  of,  360 
lymphatics  of,  361 
milk  of,  361 
Mantle  fibers,  63 
Marginal  thread  of  spermatosome,  323 

zone,  75 

Marrow,  bone-,  185.     See  also  Bone-mar- 
row. 

cell,  186 
fat-,  185,  1 88 
spaces,  primary,  109 

secondary,  III 

Martinotti's  cells  of  cerebral  cortex,  377 
Mast-cell  granules,  technic  of,  205 
Matrix  of  areolar  connective  tissue,  93 
of  cartilage,  99 
of  nail,  355 

sulcus  of,  355 

Mayer's  picric-magnesia-carmin,  44 
Median  disc  of  Hensen,  127 
Mediastinum  testis,  325 
Medullary  cords,  179 

cortex,  projection  fibers  of,  378 
rays,   288 
sheath,    142 

technic,  397-399 

substance,  association  fibers  of,  378 
centripetal  fibers  of,  378 
commissural  fibers  of,  378 
of  cerebellar  cortex,  375 

climbing  fibers  of,  375 
mossy  fibers  of,  375 
of  cerebral  cortex,  378 
of  hair,  351 
of  kidney,  288 
of  ovary,  306 
terminal  fibers  of,  378 
Medullated  nerve-fibers,  144 
Meissner's  corpuscles,  155 

technic  of,  364 
plexus,  255 

Membrana  capsulopupillaris,  429 
praeformativa,  220 
prima  of  epithelium,  75 
propria,  84 
pupillaris,  429 
tectoria  Cortii,  447,  451 
Membranous  labyrinth,  439,  440 
Meninges  of  central  nervous  system,  393 
Merkel's  terminal  disc,  127 
Mesameboid  cells,  74 
Mesenchyme,  74 
Mesoderm,  51,  73 

cells  of,  74 

Mesothelial  and  endothelial  cells,  relations 
of,  87 


Mesothelium,  74,  85 

Metakinesis,  62 

Metaphases,  57,  62 

Methylene-blue  for  staining  of  nerve-fibers, 

403 

Methyl-green,  43 
Metschnikoff' s  phagocytes,  53 
Microscope  and  its  accessories,  17 

coarse  adjustment  of,  18 

compound,   17 

description  of,  17 

fine  adjustment  of,  1 8 

parts  of,  17 

simple,  17 
Microscopic  preparation,  2O 

technic,  introduction  to,  17 
Microtome,  30 

knife,  honing  of,  36 
sharpening  of,  36 

laboratory,  31 

rocking,  31 

sliding,  31 

cutting  celloidin  sections  with,  33 

paraffin  sections  with,  31 
freezing  apparatus  for,  35 
of  Jung,  33,  34 

varieties  of,  37 
Migratory  cells,  94,  96,  175 
Milk,  361 
Mitosis,  57 

demonstration  of,  69 

heterotypic  form  of,  64 

homeotypic,  64 
Mitotic  cell-division,  diagrammatic,  58 

of  fertilized  whitefish  eggs,  60 
Mixed  gland,  230 

lateral  column,  370 
Modiolus,  443 

Molecular  movement  of  cells,  53 
Moll's  ciliary  glands,  430 

glands,  ciliary,  357 
Monaster,  62 

Mononuclear  eosinophile  cells,  187 
Monostratified  cells  of  retina,  425 
Montgomery's  glands,  361 
Morgagni's  hydatids,  322 
Morula  mass,  73 
Mother  skein,  6 1 

Motor  endings  in  striated  voluntary  mus- 
cle, 150 

end-plate,  148 

nerve-endings,  147 

neurones,  138 

peripheral,  diagram  of,  148 
Mounting,  21,  46 

Altmann's  method  of,  71 
Mouth,  small  glands  of,  231 
Muchematein,  271 
Mucicarmin,  271 
Mucosa  of  oral  cavity,  21 1 
Mucous  glands,  228 

membrane  of  intestine,  236 
Muller's  fibers,  415 
of  retina,  422 

fluid,  24 
Multicellular  glands,  82 


494 


INDEX. 


Muscle-casket,  127 
Muscle-cell,  123 

cardiac,  132 

heart,  149 

nonstriated,  124,  149 

of  fibers  of  Purkinje,  132 

smooth,  124 

striped,  123 

unstriped,  123 

Muscle-columns  of  Kolliker,  126 
Muscle-fasciculi,  129 
Muscle-fibers,  striped,  124 
Muscular  tissue,  123 
technic  of,  132 

Muscularis  mucosae  of  intestine,  236 
of  pharynx,  234 
of  small  intestine,  246 
Myelin  sheath,  142 
Myelocytes,  186 
Myeloplaxes,  187 
Myoblasts,  131 
Myocardium,  191 


NAIL,  355 
bed,  355 

sulcus  of,  355 
body  of,  355 
lunula  of,  356 
matrix,  355 

sulcus  of,  355 
root,  355 
walls,  355 
Nasal  artery,  inferior,  of  retina,  427 

superior,  of  retina,  427 
cavity,  456 

technic  of,  457 
duct,  433 
vein,  inferior,  of  retina,  427 

superior,  of  retina,  427 
Nerve,  auditory,  452 

end- organs,  neuromuscular,  158 
axial  sheath  of,  159 
distal  polar  region  of,  1 59 
equatorial  region  of,  159 
intrafusal  fibers  of,  159 
proximal  polar  region  of,  159 
neurotendinous,  162 

end-organs  of  Golgi-Mazzoni,  350 
of  Grandry,  350 
of  Herbst,  159 
of  Krause,  154 
of  Meissner,  155 
of  Ruffini,  350 

optic,  425.     See  also  Optic  nerve. 
pilomotor,  355 

Nerve-cell,  134.     See  also  Ganglion  cell. 
Nerve-ending,  annulospiral,  162 
flower-like,  162 
motor,  147 
sensory,  151 

encapsulated,  152,  154 
free,  152 

Nerve-fiber  layer  of  retina,  425 
Nerve-fibers,  142 


Nerve-fibers  ending  in  muscle  tissue,  telo- 
dendria  of,  147 

medullated,  144 

nonmedullated,  145 

staining  of,  with  methylene-blue,  403 
Nerve-trunk,  peripheral,  diagram  to  shew 

composition  of,  146 
Nervous  system,  central,  365 
blood-vessels  of,  397 
membranes  of,  393 
technic  of,  397 

tissue,  133 

technic  of,  164 

tunic  of  eye,  407,  418 
Neura,  134 
Neuraxones,  134 
Neurilemma,  143 

nuclei,  143 
Neurites,  134 
Neuroblasts,  133 
Neurodendron,  134 
Neuro-epithelial  cells,  85 
Neuro-epithelium,  85 
Neuroglia,  392 

staining  of,  406 
Neurogliar  cells,  393 
Neurokeratin,  142 
Neuromuscular  nerve  end-organs,  158.    See 

also  Nerve  end-organs^  neuromuscular. 
Neurone,  134 

cell-bodies  of,  134.  See  also  Ganglion  cell. 

centripetal,  peripheral,  139 

motor,  138 

peripheral,  diagram  of,  148 

relationship  of,  389 

sensory,  peripheral,  139 

diagram  of,  152 
Neuroplasm,  142 
Neuropodia,  136 

Neurotendinous  nerve  end-organs,  162 
Neutrophile  granules,  174 
technic  of,  206 

mixture,  Ehrlich's,  206 
Nitric  acid,  aqueous  solution  of,  as  decal- 
cifying fluid,  122 
as  fixing  solution,  24 
Nodes  of  Ranvier,  143 

demonstration  of,  164 
Nodules,  177 

cortical,  179 

lymph-,  177.     See  also  Lymph-nodules. 

secondary,  175,  178 

terminal,  of  spermatosome,  323 
Nonmedullated  fibers,  demonstration  of,l66 

nerve-fibers,  145 

Nonstriated  muscle-cell,  124,  149 
Normoblasts,  186 
Nuclear  division,  56 

membrane,  5° 

sap,  55 

stains,  40 

Nucleated  red  blood-cells  containing  hemo- 
globin, 186 
Nucleolus,  51 

true,  56 
Nucleoplasm,  55 


INDEX. 


495 


Nucleus,  51,  55 
dorsalis,  367 
segmentation,  65 

Nuel's  space,  450 


OBJECTIVE  system,  19 
Ocular  lens,  19 
Odontoblasts,  215,  2 1 6,  218 
Oil  of  bergamot  as  clearing  fluid,  47 
of  cloves  as  clearing  fluid,  47 
of  origanum  as  clearing  fluid,  47 
Olfactory  bulb,  379 

glomerular  layer,  379 
granular  layer,  380 
layer  of  mitral  cells,  379 
of  peripheral  fibers,  379 
of  pyramidal  cells,  379 
molecular  layer  of,  379 
stratum  gelatinosum,  379 
cell,  456 
hairs,  457 

region  of  nasal  cavity,  456 
Oocytes,  312 
Oppel  method  for  demonstrating  reticular 

liver  fibers,  274 
Optic  cup,  408 
nerve,  407,  425 

blood-vessels  of,  426 
papilla,  420 
region  of,  420 
stalks,  408 
vesicles,  primary,  407 

secondary,  408 
Ora  serrata,  422 
Oral  cavity,  21 1 
glands  of,  227 
technic  of,  269 
Orbiculus  ciliaris,  414 
Orcein  as  stain  for  connective  tissue,  Il8 
Organ  of  Corti,  447.  See  also  Corti's organ. 
Organs,  blood-forming,  1 68 
Osmic  acid  as  fixing  solution,  22 

for  cartilage,  120 
Osseous  labyrinth,  439 
Ossification,  107 
centers  of,  107 
groove,  112 
ridge,  112 
Osteoblasts,  109 
Osteoclasts,  in 
Otolithic  membrane,  442 
Otoliths,  442 
Outer  fiber  layer  of  retina,  420 

molecular  layer  of  retina,  420,  423 
Ova,  65 

primitive,  307 
Ovary,  306 

blood-vessels  of,  316 
cortex  of,  306 
germinal  epithelium  of,  307 
medullary  substance  of,  306 
stroma  of,  306 
technic  of,  340 
Ovula  Nabothi,  318 
Ovum,  306 


Ovum,  changes  in,  during  development,  311 

ripe,  312 

technic  of,  340 
Oxychromatin  granules,  56 
Oxyntic  cells,  238 


PACCHIONIAN  bodies,  395 
Pacinian  corpuscles,  technic  of,  364 
Pal's  method  for  demonstration  of  medul- 
lary sheath,  398 
Pancreas,  265 

blood  supply  of,  268 

interlobular  duct  of,  266 

intermediate  tubule  of,  266 

intertubular  cell-masses  of,  267 

nerve  supply  of,  268 

technic  of,  274 
Pancreatic  duct,  265 
Panniculus  adiposus,  346 
Papilla  spiralis  cochleae,  44! 
Papillse,  78 

circumvallate,  223,  225 

dentinal,  217 

filiform,  222 

foliate,  223 

fungiform,  222 

hair,  351 

lingual,  221 

optic,  420 

region  of,  420 

tactile,  345 

vascular,  345 

Papillary  artery,  inferior,  426 
superior,  426 

vein,  inferior,  426 

superior,  426 
Paracarmin  as  stain,  40 
Paradidymis,  329 
Paraffin  imbedding,  26 
diagram  for,  28 

infiltration,  26 
diagram  for,  28 

removal  of,  40 

sections,  cutting  of,  with  sliding  micro- 
tome, 31 
distilled  water  for  fixing  of,  to  slide, 

38 
fixing  of  large  number  to  cover- slips, 

39 
glycerin -albumin  for  fixing  of,  to  slide, 

38 

Japanese  method  of  fixing  to  slide,  39 
Paralinin,  55 
Paranuclein,  56 
Paraplasm,  53,  81 
Parathyroid  glands,  285 
Parenchymatous  tissues,  sectioning  of,  21 
Parietal  cells,  238 
Paroophoron,  322 
Parotid  gland,  228 
Pars  ciliaris  retinae,  414,  422 

iridica  retinae,  422 

papillaris,  344 

reticularis,  344 
Partsch's  cochineal  solution,  41 


496 


INDEX. 


Pellicula,  54 

Pelvis  of  kidney,  300 

renal,  299,  300 
Penis,  332 

erectile  tissue  of,  333 

nerve  supply  of,  334 
Perforating  fibers  of  cornea,  41 1 
Periaxial  lymph-space,  160 
Pericardium,  191 
Pericellular  plexuses,  386 
Perichondrium,  loi 
Perichoroidal  lymph-spaces,  413 
Perilymph  of  cochlea,  454 
Peri  lymphatic  spaces,  20 1 
Perimysium,  129 
Perineurium,  146 
Periosteum,  203 
Peripheral  centripetal  neurones,  139 

motor  neurone,  diagram  of,  148 

nerve  terminations,  147 

sensory  neurones,  139 

diagram  of,  152 
Peritendineum,  97 
Perivascular  spaces,  20 1 
Petit  and  Ripart's  solution,  21 
Pe tit's  canal,  428 
Pfliiger's  primary  egg  tubes,  307 
Phagocytes,  175 

MetschnikofF  s,  53 
Phalangeal  plate,  449,  450 

process,  449 
Pharynx,  233 

Physiologic  excavation  of  retina,  420 
Pia  intima,  395 

mater,  395 
Pial  funnels,  396 
Picric  acid  as  fixing  solution,  23 

for  cell,  69 
as  stain,  44 
Picric-magnesia-carmin  as  stain,  Mayer's, 

44 

Picric-nitric  acid  as  fixing  solution,  23 
Picric-osmic-acetic  acid   solution  as  fixing 

fluid,  24 

Picric-sublimate-osmic  acid  solution  as  fix- 
ing fluid,  24 
Picrocarmin  as  stain  for  connective  tissue 

in  cartilage,  120 
for  elastic  fibers  in  cartilage,  I2O 

of  Ranvier,  43 

of  Weigert,  43 

Picrosulphuric  acid  as  fixing  solution,  23 
Pigment,  90 

cell,  71,  95,  96 

in  epidermis,  346 

layer  of  eye,  418 

membrane,  408 
of  eye,  407 

origin  of,  346 
Pillar  cells,  448 

heads  of,  448 
Pilomotor  nerves,  355 
Pineal  gland,  380 
Pituitary  body,  381 
Plasma  cells,  96 
Plexus,  choroid,  396 


Plexus,  epilamellar,  232 

ground,  of  cornea,  412 

hypolamellar,  232 

intracapsular,  387 

myentericus,  254 

of  Auerbach,  254 

of  Heller,  251 

of  Meissner,  255 

pericellular,  386 

subepithelial,  of  cornea,  412 

superficial,  of  cornea,  412 
Plicae  palmatse,  318 

semilunares,  250 

sigmoideae,  237 

transversales  recti,  250 
Plural  staining,  43 
Polar  body,  65 

field,  64 

rays,  62 

Polarity  of  cell,  75 

Polygonal  cells  of  cerebral  cortex,  376 
Polykaryocyte,  175 

Polymorphous  cells  of  cerebral  cortex,  377 
Polynuclear  cells,  64 

leucocytes,  64 

Polystratified  cells  of  retina,  425 
Portal  vein,  260 
Posterior  elastic  membrane  of  cornea,  41 1 

epithelium  of  iris,  416 

hyaloid  arteries,  429 
Potassium  bichromate-osmic  acid  solution, 

400 
Precapillary  arteries,  196 

veins,  197 
Precartilage,  99 
Primary  blastodermic  layers,  73 

germ  layers,  73 

marrow  spaces,  109 

optic  vesicles,  407 

tendon  bundles,  96 
Primitive  ova,  307 

seminal  cells,  334 
Primordial  ova,  307 
Prominentia  spiralis,  446 
Promontory  ridge,  439 
Pronucleus,  female,  67 

male,  67 

Prophases,  57,  60 
Prostate,  330 

blood-vessels  of,  332 

nerve  supply  of,  332 

secretion  of,  332 
Prostatic  bodies,  332 

concretions,  332 
Protoplasm,  51,  8 1 
Protoplasmic  currents,  68 

stains,  40 
Protozoa,  51 
Pseudopodia,  53 
Pulp  cords  of  spleen,  182 
Pupil,  dilator  muscle  of,  416 

sphincter  muscle  of,  416 
Purkinje's  cells,  138 

of  cerebellar  cortex,  374 

fibers,  190 

muscle-cells  of,  132 


INDEX. 


497 


Purkinje's  vesicle,  306 

Purpurin,    alkaline,    as   stain   for  calcium 

carbonate  in  bone,  122 
Pyramidal  cells,  large,  of  cerebral  cortex, 

376 

of  cerebral  cortex,  138 
small,  of  cerebral  cortex,  376 
columns,  crossed,  370 
tract,  direct,  370 
Pyramids  of  Ferrein,  289 


QUINTUPLE  hydroquinon  developer,  401 


RABL'S  hematoxylin-safranin  stain,  44 

solution,  24 
Kami  cochleares,  452 

vestibulares,  452 

Ram6n  y  CajaFs  technic  for  retina,  435 
Ranvier's  crosses,  164,  165 

iodin  and  potassium  iodid  solution,  21 

method  for  demonstrating  spaces  in  bone, 

121 

for  examination  of  connective  tissue, 

117 
nodes,  143 

demonstration  of,  164 
picrocarmin,  43 
Real  image,  19 
Recessus  camene  posterioris,  427 

cochleae,  454 
Rectum,  249 
Red     blood-cells,    nucleated,    containing 

hemoglobin,  186 
blood-corpuscles,  169 
bone-marrow,  185 
Reissner's  membrane,  444,  447 
Relationship  of  neurones,  389 
Remak's  fibers,  145 

demonstration  of,  1 66 
Renal  lobes,  287 

pelvis,  299,  300 
Renflement  biconique,  143 
Respiration,  organs  of,  275 

technic  of,  286 
Respiratory  bronchioles,  279 
epithelium,  280 
region  of  nasal  cavity,  456 

accessory  cavities  of,  456 
Rete  testis,  325,  327 
Retia  mirabilia,  199 
Retina,  407,  408,  418 
blood-vessels  of,  426 
layers  of,  418-420,  423 
macula  lutea  of,  421 
Miiller's  fibers  of,  422 
optic  papilla  of,  420 
ora  serrata  of,  422 
pars  ciliaris  retinae,  422 

iridica  retinae,  422 
relation  of  elements  of,  to  one  another, 

423 

technic  of,  434 
Retinaculae  cutis,  346 
Retzius,  end-piece  of,  323 
32 


Ribbon  sectioning,  32 

Ripart  and  Petit' s  solution,  21 

Ripe  ova,  312 

Rocking  microtome,  31 

Rod-fibers  of  retina,  419 

Rod-visual  cells,  418 

Rolando's  gelatinous  substance,  367 

Root-sheaths  of  hair,  351.    See  also  Hair, 

root-sheaths  of. 

Rose's  carmin-bleu  de  Lyon,  44 
Rouleaux,  169,  170 
Rudder  membrane  of  spermatosome,  323 


SACCULAR  glands,  84 

Sacculus,  440,  441,  454 

Saccus  endolymphaticus,  440,  454 

Safranin  as  stain,  43 

Salivary  glands,  228 

blood-supply  of,  232 
lymphatics  of,  232 
nerve  supply  of,  232 
scheme  of,  227 
Sarcolemma,  125 
Sarcolytes,  131 
Sarcous  elements,  126,  128 
Scala  media,  444 

tympani,  444 

vestibuli,  444 
Schlemm's  canal,  409 
Schmidt  -  Lantermann-Kuhnt's    segments, 

142 

Schultze's  iodized  serum,  21 
Schwann's  sheath,  143 
Sclera,  407,  409 

blood-vessels  of,  410 

technic  of,  434 
Scleral  conjunctiva,  409 

sulcus,  inner,  410 
Sebaceous  glands,  358 
Secondary  marrow  spaces,  III 

nodule,  175,  178 

optic  vesicle,  408 

tendon  bundles,  97 
Secretion  of  intestine,  256 

process  of,  84 

vacuoles,  259 
Section  staining,  40 

stretchers,  35 
Sectioning,  21,  30 

double  knife  for,  21 

free-hand,  21 

of  parenchymatous  tissues,  21 

ribbon,  32 
Segmentation  cell,  64 

nucleus,  65 
Selective  stains,  40 
Semen,  323 

technic  of,  340 
Semicircular  canals,  442 

anterior  superior  vertical,  440 
external,  440 
horizontal,  440 
posterior  inferior  vertical,  440 
Semilunar  fold,  443 

valves,  191 


498 


INDEX. 


Seminal  cells,  primitive,  334 

vesicles,  330 
Sense  cells,  75 

Sense-organs,  special,    general   considera- 
tions of,  458 

Sensory  nerve-endings,  151 
encapsulated,  152,  154 
free,  152 

neurones,  peripheral,  diagram  of,  152 
Septa  renis,  289 
Septum  posticum,  395 
Serous  cavities,  201 

gland,  228 
Sertoli's  cells,  326 
Sexual  cells,  matured,  65 
Sharpening  microtome  knife,  36 
Sharpey,  fibers  of,  106 
Sheath  of  Schwann,  143 
Sihler's   method   of   demonstrating  nerve- 
endings,  167 

Silver-impregnation  of  thin  membranes,  49 
Simple   epithelium,  76.     See  also  Epithe- 
lium, simple. 

microscopes,  17 
Sinus,  199 

blood,  199 

lactiferus,  360 

pocularis,  332 
Skin,  341 

and  appendages,  341 
technic  of,  362 

blood-vessels  of,  350 

glands  of,  357 

nerve-endings  in,  348 

nerves  of,  348 

pigment  of,  technic  of,  363 

structure  of,  technic  of,  363 

technic  of,  362 

true,  341 

vascular  system  of,  347 
Slides,  20 

Sliding  microtome,  31.     See  also  Micro- 
tome, sliding. 
Small  intestine,  243.     See  also  Intestine, 

small. 
Smell,  organ  of,  456 

technic  of,  457 
Sole  nuclei,  148 

plate,  granular,  148 
Solitary  lymph-follicles,  177 
Somatic  cell,  65 
Soudan  III  as  stain  for  fat,  I2O 
Special  histology,  1 68 

sense-organs,  general  considerations  of, 

458 
Specimens,  drawing  of,  20 

examination  of,  19 

permanent,  preparation  of,  46 
Sperma,  323 
Spermatids,  66,  336 

development  of,  into  spermatosomes,  336 
Spermatoblast,  338 
Spermatocytes,  66 

of  first  order,  335 
Spermatogenesis,  334 
Spermatogones,  66 


Spennatogonia,  334 
Spermatosome,  323 

accessory  thread  of,  323 

axial  thread  of,  323 
sheath  of,  323 

development  of,  from  spermatids,  336 

flagellum  of,  323 

head  of,  323 

marginal  thread  of,  323 

middle  piece  of,  323 

rudder  membrane  of,  323 

tail  of,  323 

terminal  nodule  of,  323 

undulating  membrane  of,  323 
Spermatozoa,  53>  65,  66 
Spermatozoon,  323.     See  also    Spermato- 
some. 

Sphincter  muscle  of  pupil,  416 
Spider-cells,  393 
Spinal  cord,  365 

anterior  median  fissure  of,  365 

gray  substance  of,  365 

horns  of,  367 

posterior  median  septum  of,  365 

structure  of,  365 

white  substance  of,  365 

ganglia,  382 

ganglion  cell  of  Dogiel,  384 
Spindle  cells  of  cerebral  cortex,  376 
Spiral  ganglion  of  cochlea,  452 
Spirem,  61 
Spleen,  180 

lobules,  182 
Splenic  pulp,  183 
Spongioblasts,  392 

diffuse,  424 

stratum  of,  424 
Spongioplasm,  53 
Staining,  40 

double,  43 

in  bulk,  45 

diagram  showing  method,  46 

in  section,  diagram  showing  method,  46 

neurofibrils      and     Golgi-nets,    Bethe's 
method  for,  405 

of  cells,  69 

of  nervous  tissue,  402 

of  neuroglia,  406 

plural,  43 

purpose  of,  40 

section,  40 
Stains,  40 

acid,  40 

alkaline  purpurin,  for  calcium  carbonate 
in  bone,  122 

alum-carmin,  41 

anilin,  42 

basic,  40 

Bismarck  brown,  43 

borax-carmin,  alcoholic,  40 
aqueous,  40 

carmin,  40 

carmin-bleu  de  Lyon,  of  Rose,  44 

coal-tar,  42 

Czocor's  cochineal  solution,  41 

Ehrlich-Biondi  triple,  45 


INDEX. 


499 


Stains  for  adipose  tissue,  119 

gold  chlorid,   for  capsules  of  cartilage, 

120 

hemalum,  42 
hematoxylin,  41 
Bohmer's,  41 
Delafield's,  41 

for   demonstrating  canalicular   sys- 
tem in  cartilage,  120 
Ehrlich's,  42 

for  lime-salts  in  bone,  122 
Friedlander' s  glycerin-,  42 
Heidenhain's  iron,  42 
hematoxylin-eosin,  44 
hematoxylin-safranin  of  Rabl,  44 
iodo-iodid  of  potassium,  to  demonstrate 

glycogen  in  cartilage,  1 21 
magenta  red,  for  connective  tissue,  119 
methyl-green,  43 
nuclear,  40 

orcein,  for  connective  tissue,  1 18 
paracarmin,  40 

Partsch's  cochineal  solution,  41 
picric  acid,  44 

picric-acid-fuchsin,  Van  Gieson's,  399 
picric-magnesia-carmin,  Mayer's,  44 
picrocarmin,  for  connective  tissue  in  car- 
tilage, 120 

for  elastic  fibers  in  cartilage,  120 
Ranvier's,  43 
Weigert's,  43 
protoplasmic,  40 
safranin,  43 
selective,  40 
Soudan  III,  for  fat,  I2O 
Stellate  cells,  262 

large,  of  cerebellar  cortex,  375 
of  cerebellar  cortex,  374 
of  cerebral  cortex,  376 
Stellulse  vasculosoe,  414 
Stomach,  235,  237 

technic  of,  271 
Stomata,  85 

Straight  tubules  of  testis,  325 
Stratified  epithelium,  77 
Stratum  circulare,  437 
corneum,  343 
gelatinosum,  379 
germinativum,  341 
granulosum,  309,  341 
lucidum,  343 

technic  of,  362 
Malpighii,  341 

technic  of,  363 
proprium  of  oral  cavity,  211 
radiatum,  437 
spinosum,  342 
spongioblasts,  424 
submucosum  of  oral  cavity,  212 
Stria  vascularis,  446 
Striation  of  Baillarger,  379 

of  Bechtereff  and  Kaes,  379 
Striped  muscle-cell,  123 

muscle-fibers,  124 
Stroma  of  red  blood-cells,  169,  170 
of  iris,  416 


Stroma  of  ovary,  306 
Subarachnoid  space,  394 
Subdural  space,  394 
Subepithelial  plexus  of  cornea,  412 
Sublingual  gland,  228 
Submaxillary  gland,  230 
Submucosa  of  intestine,  236 

of  oral  cavity,  212 
Subpia,  396 
Substantia  gelatinosa,  367 

propria  of  cornea,  410 
Succus  prostaticus,  332 
Sudoriferous  duct,  357 
Sudoriparous  glands,  357 
Sulcus  of  matrix  of  nail,  355 

scleral,  inner,  410 

spiralis  internus,  446 
Superficial  plexus  of  cornea,  412 
Superior  nasal  artery  of  retina,  427 
vein,  427 

papillary  artery,  426 

vein,  426 

Suprarenal  glands,  301 
blood-vessels  of,  303 
nerves  of,  304 
technic  for,  305 

Suspensory  ligament  of  lens,  428 
Sustentacular  cells,  85,  224,  334 

fiber  of  Deiters'  cells,  450 
Sweat-glands,  357 

nerves  of,  358 
Sympathetic  ganglia,  140,  385 


TACTILE  papillae,  345 
Taeniae  coli,  236 

of  large  intestine,  250 
Tapetum  cellulosum,  413 

fibrosum,  413 
Taste-buds,  223 
Taste-pore,  224 
Teasing,  20 

Technic,  microscopic,  introduction  to,  17 
Teeth,  213 

adult,  structure  of,  213 

auditory,  446 

development  of,  217 

pulp  of,  215 
Tegmental  cells,  224 
Teichmann's  crystals,  169 

isolation  of,  207 
Tela  submucosa,  212 
Telodendria,  135 

of  nerve-fibers  ending  in  muscle  tissue, 

H7 

Telodendrion,  147,  151 
Telolemma  nuclei,  148 
Telophases,  57,  64 

Temperature,  effects  of,  on  tissues,  27 
Tendons,  96 

bundles,  primary,  96 
secondary,  97 

fasciculi,  96 

spindle,  Golgi,  162 
Tenon's  capsule,  409 
Terminal  disc  of  Merkel,  127 


INDEX. 


Terminal  ledges,  80 

nodule  of  spermatosome,  323 
Testes,  324 

blood-vessels  of,  329 
lymphatics  of,  329 
nerve-supply  of,  329 
technic  of,  340 
Theca  folliculi,  309 
Thoma's  ampullae,  182 
Thymus  gland,  1 88 
Thyroid  gland,  284 
Tigroid  granules,  134 
Tissue,  73 
adipose,  99 

stains  for,  119 
connective,  89 
areolar,  93 

cellular  elements  of,  94 
ground- substance  of,  93 
matrix  of,  93 
fibrous,  93 
mucous,  92 
Ranvier's  method  for  examination  of, 

117 

reticular,  92 
technic  of,  117 
effects  of  temperature  on,  27 
epithelial,  74 
erectile,  of  penis,  333 
fibrous,  elastic,  98 
frozen    with   carbon   dioxid,  cutting  of, 

35,  36 

lymphoid,  177 

muscular,  123 
technic  of,  132 

nervous,  133 

technic  of,  164 
Toluol  as  clearing  fluid,  47 
Tomes'  granular  layer,  220 

processes,  218 
Tongue,  221 

lymph-follicles  of,  225 
Tonsils,  lymph-follicles  of,  225 
Tooth-pulp,  215 
Trabecube  of  liver,  258 
Trachea,  276 

Transitional  eosinophile  cells,  187 
Transverse  disc,  127 

membrane  of  Krause,  127 
Triangular  cells  of  cerebral  cortex,  376 
Trophoplasts,  347 

Trypsin   digestion  for  differentiating  con- 
nective and  elastic  tissues,  n8 
Tubular  glands,   82.      See   also    Glands, 

tubular. 
Tubule,  dentinal,  214 

intermediate,  of  pancreas,  266 

straight  collecting,  of  kidney,  288 

uriniferous,  287,  293 

schematic  diagram  of,  297 
Tubuli  recti  of  testis,  325 
Tunica  albuginea,  84,  324 

dartos,  346 

externa  of  eye,  407 

fibrosa  oculi,  407,  409 

interna  of  eye,  407,  418 


Tunica  media  of  eye,  407,  412 

mucosa  of  intestine,  236 

propria  of  oral  cavity,  211 

sclerotica,  407,  409.     See  also  Sclera. 

vaginalis,  324 

vasculosa,  324 

of  eye,  407,  412 
Tunnel  of  Corti,  448 
Tunnel-fibers,  452 
Tiirck's  column,  370 

Tympanic  investing  layer  of  basilar  mem- 
brane, 447 

membrane,  436 
layers  of,  436 
Tympanum,  437 
Tyson's  glands,  334 


UNDULATING  membrane  of  spermatosome, 

323 

Unstriped  muscle-cell,  123 
Ureter,  299,  300 
Urethra,  epithelium  of,  333 

submucosa  of  cavernous  portion  of,  333 
Urinary  organs,  287 
technic  for,  305 
Uriniferous  tubules,  287,  293 

schematic  diagram  of,  297 
Uterus,  317 

blood  supply  of,  319 

layers  of,  318 

lymphatics  of,  319 

nerve  supply  of,  320 

technic  of,  340 
Utriculosaccular  duct,  440 
Utriculus,  440,  441,  454 

wall  of,  442 


VACUOLES,  54 

secretion,  259 
Vagina,  320 

sensory  nerve-endings  in,  322 

technic  of,  340 

vestibule  of,  322 
Valvulae  conniventes,  236 
Van  Gieson's  picric-acid-fuchsin  stain,  399 
Vas  aberrans  Halleri,  328 

deferens,  329 

epididymidis,  326,  328 

spirale,  447 
Vasa  afferentia,  178,  296 

efferentia,  178,  325,  327 

recta  spuria,  297 
Vascular  canals,  103 

papillae,  345 

system,  190 

tunic  of  eye,  407,  412 
Vater-Pacinian  corpuscles,  157 
Veins,  197 

central,  258 

intralobular,  258,  261,  298 

portal,  260 

precapillary,  197 

smaller,  197 

valves  of,  198 


INDEX. 


501 


Venae  arciformes,  298 

stellatce,  298 

vorticosae,  413 
Ventrolateral  column,  367 
Ventromesial  column,  367 
Venuloe  rectae,  298 
Vesicula  prostatica,  332 
Vestibular  membrane,  444,  447 
Vestibule  of  ear,  439 

of  nasal  cavity,  456 

of  vagina,  322 

Villi   of  mucous  membrane  of  small  in- 
testine, 243 

of  small  intestine,  lacteals  of,  253 
Virchow's  bone  corpuscles,  104 

isolation  of,  123 
Virtual  image,  19 
Visual  cells,  418 
Vitreous  body,  407,  427 

membrane,  412,  414 
Volkmann's  canals,  106 
von  Ebner's  process  of  decalcification,  122 
von  Koch's  technic  for  bone,  123 


WAGNER'S  spot,  306 
Wandering  cells,  53,  94,  96 
Water,  distilled,  for  fixing  paraffin  sections 
to  slide,  38 


Weigert's   methods    for  demonstration 
medullary  sheath,  397,  398 

picrocarmin,  43 
Wharton's  jelly,  92 
White  blood-corpuscles,  173 

fibers,  90 

fibrocartilage,  IO2 

rami  communicantes,  387 
fibers,  387 

substance  of  spinal  cord,  365 
Wirsungian  duct,  265 
Wolffian  duct,  322 


XYLOL  as  clearing  fluid,  47 
as  intermediate  fluid,  26 


YELLOW  bone-marrow,  185,  188 
Yolk  granules,  311 


ZENKER'S  fluid,  25 
Zinn's  arterial  circle,  426 

zonule,  428 
Zona  pellucida,  311 
Zonula  ciliaris,  407,  428 
Zonule  of  Zinn,  428 


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Abbott  on  Transmissible  Diseases,    second  Edition,  Revised. 

The  Hygiene  of  Transmissible  Diseases :  their  Causation,  Modes  of 
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Professor  of  Hygiene  and  Bacteriology,  University  of  Pennsylvania. 
Octavo,  351  pages,  with  numerous  illustrations.  Cloth,  $2.50  net. 


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Anders*  Practice  of  Medicine.       Fifth  Revised  Edition. 

A  Text-Book  of  the  Practice  of  Medicine.  By  JAMES  M.  ANDERS, 
M.  D.,  PH.  D.,  LL.  D.,  Professor  of  the  Practice  of  Medicine  and  of 
Clinical  Medicine,  Medico-Chirurgical  College,  Philadelphia.  Hand- 
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Bastin's  Botany. 

Laboratory  Exercises  in  Botany.  By  EDSON  S.  BASTIN,  M.  A.,  late 
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Beck  on  Fractures. 

Fractures.  By  CARL  BECK,  M.  D.,  Surgeon  to  St.  Mark's  Hospital  and 
the  New  York  German  Poliklinik,  etc.  With  an  appendix  on  the  Prac- 
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Beck's  Surgical  Asepsis. 

A  Manual  of  Surgical  Asepsis.  By  CARL  BECK,  M.  D.,  Surgeon  to  St. 
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Boisliniere's    Obstetric  Accidents,   Emergencies,  arid 
Operations. 

Obstetric  Accidents,  Emergencies,  and  Operations.  By  L.  CH.  Bois- 
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Bohm,  Davidoff,   arid  Huber's  Histology. 

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Butler's  Materia  Medica,  Therapeutics,  arid  Pharma- 
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Cerna  on  the  Newer  Remedies,    second  Edition,  Revised. 

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Chapin  on  Insanity. 

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Chapman's   Medical    Jurisprudence  and  Toxicology. 

Second  Edition,  Revised. 

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M.  D.,  Professor  of  Institutes  of  Medicine  and  Medical  Jurisprudence, 
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Church  and  Peterson's  Nervous  and  Mental  Diseases. 

Third  Edition,  Revised  and  Enlarged. 

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fessor of  Nervous  and  Mental  Diseases,  and  Head  of  the  Neurological 
Department,  Northwestern  University  Medical  School,  Chicago;  and 
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Clarkson's  Histology. 

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Corwin's  Physical  Diagnosis.    Third  Edition,  Revised. 

Essentials  of  Physical  Diagnosis  of  the  Thorax.  By  ARTHUR  M. 
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Crookshank's  Bacteriology.     Fourth  Edition,  Revised. 

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London.  Octavo,  700  pages,  273  engravings  and  22  original  colored 
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Surgery.       Third  Edition,  Revised. 

Modern  Surgery,  General  and  Operative.  By  JOHN  CHALMERS  DA 
COSTA,  M.  D.,  Professor  of  Principles  of  Surgery  and  Clinical  Surgery, 
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Enlarged  by  over  200  Pages,  with  more  than  100  New  Illustrations. 


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Davis's  Obstetric  Nursing. 

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delphia Hospital.  i2mo  volume  of  400  pages,  fully  illustrated. 
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DeSchweinitz  on  Diseases  qf  the  Eye.  Third  Edition,  Revised. 

Diseases  of  the  Eye.  A  Handbook  of  Ophthalmic  Practice.  By  G. 
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Dorland's  Dictionaries. 

[See  American  Illustrated  Medical  Dictionary  and  American 
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Modern  Obstetrics.  By  W.  A.  NEWMAN  DORLAND,  M.  D.,  Assistant 
Demonstrator  of  Obstetrics,  University  of  Pennsylvania;  Associate  in 
Gynecology,  Philadelphia  Polyclinic.  Octavo  volume  of  797  pages, 
with  201  illustrations.  Cloth,  $4.00  net. 

Eichhorst's  Practice  qf  Medicine. 

A  Text-Book  of  the  Practice  of  Medicine.  By  DR.  HERMAN  EICHHORST, 
Professor  of  Special  Pathology  and  Therapeutics  and  Director  of  the 
Medical  Clinic,  University  of  Zurich.  Translated  and  edited  by  AUGUS- 
TUS A.  ESHNER,  M.  D.,  Professor  of  Clinical  Medicine,  Philadelphia 
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Friedrich  and  Curtis  on  the  Nose,  Throat,  and  Ear. 

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eral Medicine.  By  DR.  E.  P.  FRIEDRICH,  of  Leipzig.  Edited  by  H. 
HOLBROOK  CURTIS,  M.  D.,  Consulting  Surgeon  to  the  New  York  Nose 
and  Throat  Hospital.  Octavo,  348  pages.  Cloth,  $2.50  net. 

Frothingham's  Guide  for  the  Bacteriologist. 

Laboratory  Guide  for  the  Bacteriologist.  By  LANGDON  FROTHINGHAM, 
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Scientific  School,  Yale  University.  Illustrated.  Cloth,  75  cts.  net. 

Garrigues'  Diseases  qf  Women.    Third  Edition,  Revised. 

Diseases  of  Women.  By  HENRY  J.  GARRIGUES,  A.  M.,  M.  D.,  Gyne- 
cologist to  St.  Mark's  Hospital  and  to  the  German  Dispensary,  New 
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OF   W.  B.  SAUNDERS   6-    CO. 


Gould  and  Pyle's  Curiosities  qf   Medicine. 

Anomalies  and  Curiosities  of  Medicine.  By  GEORGE  M.  GOULD,  M.D., 
and  WALTER  L.  PYLE,  M.  D.  An  encyclopedic  collection  of  rare  and 
extraordinary  cases  and  of  the  most  striking  instances  of  abnormality  in 
all  branches  of  Medicine  and  Surgery,  derived  from  an  exhaustive 
research  of  medical  literature  from  its  origin  to  the  present  day, 
abstracted,  classified,  annotated,  and  indexed.  Handsome  octavo 
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Grafstrom's  Mechano-Therapy. 

A  Text-Book  of  Mechano-Therapy  (Massage  and  Medical  Gymnastics). 
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Griffith    On    the    Baby.       Second  Edition,  Revised. 

The  Care  of  the  Baby.  By  J.  P.  CROZER  GRIFFITH,  M.  D.,  Clinical 
Professor  of  Diseases  of  Children,  University  of  Pennsylvania ;  Phy- 
sician to  the  Children's  Hospital,  Philadelphia,  etc.  i2mo,  404  pages; 
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Griffith's  Weight  Chart. 

Infant's  Weight  Chart.  Designed  by  J.  P.  CROZER  GRIFFITH,  M.  D., 
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Hart's  Diet  in  Sickness  and  in  Health. 

Diet  in  Sickness  and  Health.  By  MRS.  ERNEST  HART,  formerly  Student 
of  the  Faculty  of  Medicine  of  Paris  and  of  the  London  School  of  Medi- 
cine for  Women ;  with  an  Introduction  by  SIR  HENRY  THOMPSON, 
F.  R.  C.  S.,  M.  D.,  London.  220  pages.  Cloth,  $1.50  net. 

Haynes'  Anatomy. 

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Heisler's  Embryology.     Second  Edition,  Revised, 

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of  405  pages,  handsomely  illustrated.  Cloth,  $2.50  net. 

Hirst's    Obstetrics.       Third  Edition,  Revised  and  Enlarged. 

A  Text-Book  of  Obstetrics.  By  BARTON  COOKE  HIRST,  M.  D.,  Professor 
of  Obstetrics,  University  of  Pennsylvania.  Handsome  octavo  volume 
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Hyde  and  Montgomery  on  Syphilis  arid  the  Venereal 

Diseases.       Second  Edition,  Revised  and  Greatly  Enlarged. 

Syphilis  and  the  Venereal  Diseases.  By  JAMES  NEVINS  HYDE,  M.  D., 
Professor  of  Skin  and  Venereal  Diseases,  and  FRANK  H.  MONTGOMERY, 
M.  D.,  Associate  Professor  of  Skin,  Genito-Urinary,  and  Venereal  Dis- 
eases in  Rush  Medical  College,  Chicago,  111.  Octavo,  594  pages, 
profusely  illustrated.  Cloth,  $4.00  net. 

lite  International  Text-Book  of  Surgery.    in  TWO  volumes. 

By  American  and  British  Authors.  Edited  by  J.  COLLINS  WARREN, 
M.  D.,  LL.  D.,  F.  R.  C.  S.  (Hon.),  Professor  of  Surgery,  Harvard  Medi- 
cal School,  Boston ;  and  A.  PEARCE  GOULD,  M.  S.,  F.  R.  C.  S.,  Lecturer 
on  Practical  Surgery  and  Teacher  of  Operative  Surgery,  Middlesex 
Hospital  Medical  School,  London,  Eng.  Vol.  I.  General  Surgery.— 
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plates.  Sold  by  Subscription.  Prices  per  volume:  Cloth,  $5.00  net; 
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"  It  is  the  most  valuable  work  on  the  subject  that  has  appeared  in  some  years.  The  clini- 
cian and  the  pathologist  have  joined  hands  in  its  production,  and  the  result  must  be  a  satis- 
faction to  the  editors  as  it  is  a  gratification  to  the  conscientious  reader." — Annals  of  Surgery. 

"  This  is  a  work  which  comes  to  us  on  its  own  intrinsic  merits.  Of  the  latter  it  has  very 
many.  The  arrangement  of  subjects  is  excellent,  and  their  treatment  by  the  different  authors 
is  equally  so.  What  is  especially  to  be  recommended  is  the  painstaking  endeavor  of  each 
writer  to  make  his  subject  clear  and  to  the  point.  To  this  end  particularly  is  the  technique 
of  operations  lucidly  described  in  all  necessary  detail.  And  withal  the  work  is  up  to  date  in 
a  very  remarkable  degree,  many  of  the  latest  operations  in  the  different  regional  parts  of  the 
body  being  given  in  full  details.  There  is  not  a  chapter  in  the  work  from  which  the  reader 
may  not  learn  something  new." — Medical  Record,  New  York. 

Jackson's  Diseases  of  the  Eye. 

A  Manual  of  Diseases  of  the  Eye.  By  EDWARD  JACKSON,  A.  M.,  M.  D., 
Emeritus  Professor  of  Diseases  of  the  Eye,  Philadelphia  Polyclinic  and 
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178  illustrations,  mostly  from  drawings  by  the  author.  Cloth,  $2.50  net. 

Keating' s  Life  Insurance. 

HW  to  Examine  for  Life  Insurance.  By  JOHN  M.  KEATING,  M.  D., 
Fellow  of  the  College  of  Physicians  of  Philadelphia ;  Ex-President  of  the 
Association  of  Life  Insurance  Medical  Directors.  Royal  octavo,  211 
pages.  With  numerous  illustrations.  Cloth,  $2.00  net. 

Keen  on  the  Surgery  of  Typhoid  Fever. 

The  Surgical  Complications  and  Sequels  of  Typhoid  Fever.  By  WM. 
W.  KEEN,  M.  D.,  LL.  D.,  F.  R.  C.  S.  (Hon.),  Professor  of  the  Principles 
of  Surgery  and  of  Clinical  Surgery,  Jefferson  Medical  College,  Phila- 
delphia, etc.  Octavo  volume  of  386  pages,  illustrated.  Cloth,  $3.00  net. 

Keen's    Operation    Blank.      Second  Edition,  Revised  Form. 

An  Operation  Blank,  with  Lists  of  Instruments,  etc.,  Required  in  Vari- 
ous Operations.  Prepared  by  W.  W.  KEEN,  M.  D.,  LL.  D.,  F.  R.  C.  S. 
(Hon.),  Professor  of  the  Principles  of  Surgery  and  of  Clinical  Surgery, 
Jefferson  Medical  College,  Philadelphia.  Price  per  pad,  blanks  for  fifty 
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OF   W.  B.  SAUNDERS   &    CO. 


Kyle  on  the  Nose  and  Throat,     second  Edition. 

Diseases  of  the  Nose  and  Throat.  By  D.  BRADEN  KYLE,  M.  D.,  Clinical 
Professor  of  Laryngology  and  Rhinology,  Jefferson  Medical  College, 
Philadelphia.  Octavo,  646  pages;  over  150  illustrations  and  6  litho- 
graphic plates.  Cloth,  $4.00  net;  Sheep  or  Half  Morocco,  $5.00  net. 

Laine's  Temperature  Chart. 

Temperature  Chart.  Prepared  by  D.  T.  LAINE,  M.  D.  Size  8x13^ 
inches.  A  conveniently  arranged  Chart  for  recording  Temperature, 
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of  Typhoid  Fever.  Price,  per  pad  of  25  charts,  50  cts.  net. 

Levy,  Klemperer,  and  Eshner's  Clinical  Bacteriology. 

The  Elements  of  Clinical  Bacteriology.  By  DR.  ERNST  LEVY,  Pro- 
fessor in  the  University  of  Strasburg,  and  FELIX  KLEMPERER,  Privat- 
docent  in  the  University  of  Strasburg.  Translated  and  edited  by 
AUGUSTUS  A.  ESHNER,  M.  D.,  Professor  of  Clinical  Medicine,  Philadel- 
phia Polyclinic.  Octavo,  440  pages,  fully  illustrated.  Cloth,  $2.50  net. 


Lockwood's  Practice  tf  Medicine. 

A  Manual  of  the  Practice  of  Medicine.  By  GEORGE  ROE  LOCKWOOD, 
M.  D.,  Professor  of  Practice  in  the  Woman's  Medical  College  of  the 
New  York  Infirmary,  etc. 

Long's  Syllabus  tf  Gynecology. 

A  Syllabus  of  Gynecology,  arranged  in  Conformity  with  "An  American 
Text-Book  of  Gynecology."  By  J.  W.  LONG,  M.  D.,  Professor  of  Dis- 
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Macdonald's  Surgical  Diagnosis  and  Treatment. 

Surgical  Diagnosis  and  Treatment.  By  J.  W.  MACDONALD,  M.  D. 
Edin.,  F.  R.  C.  S.  Edin.,  Professor  of  Practice  of  Surgery  and  Clinical 
Surgery,  Hamline  University.  Handsome  octavo,  800  pages,  fully  illus- 
trated. Cloth,  $5.00  net;  Sheep  or  Half  Morocco,  $6.00  net. 

Mallory  and  Wright's  Pathological  Technique. 

Second  Edition,  Revised. 

Pathological  Technique.  A  Practical  Manual  for  Laboratory  Work  in 
Pathology,  Bacteriology,  and  Morbid  Anatomy,  with  chapters  on  Post- 
Mortem  Technique  and  the  Performance  of  Autopsies.  By  FRANK  B. 
MALLORY,  A.M.,  M.  D.,  Assistant  Professor  of  Pathology,  Harvard 
University  Medical  School,  Boston;  and  JAMES  H.  WRIGHT,  A.M., 
M.  D.,  Instructor  in  Pathology,  Harvard  University  Medical  School, 
Boston. 
•  -  ,-s  i  i,  rfc  xt_  *j  —*^  D  «.  j~4^«.:  «*  Third  Edition,  increased  in 

McFarland's  Pathogenic  Bacteria.      size  by  over  I00  Pages> 

Text-Book  upon  the  Pathogenic  Bacteria.  By  JOSEPH  MCFARLAND, 
M.  D.,  Professor  of  Pathology  and  Bacteriology,  Medico-Chirurgical 
College  of  Philadelphia,  etc.  Octavo  volume  of  621  pages,  finely  illus- 
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io  MEDICAL   PUBLICATIONS 

Meigs  on  Feeding  in  Infancy. 

Feeding  in  Early  Infancy.  By  ARTHUR  V.  MEIGS,  M.  D.  Bound  in 
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Moore's  Orthopedic  Surgery. 

A  Manual  of  Orthopedic  Surgery.  By  JAMES  E.  MOORE,  M.  D.,  Pro- 
fessor of  Orthopedics  and  Adjunct  Professor  of  Clinical  Surgery,  Uni- 
versity of  Minnesota,  College  of  Medicine  and  Surgery.  Octavo  volume 
of  356  pages,  handsomely  illustrated.  Cloth,  $2.50  net. 

Morten's  Nurses'  Dictionary. 

Nurses'  Dictionary  of  Medical  Terms  and  Nursing  Treatment.  Con- 
taining Definitions  of  the  Principal  Medical  and  Nursing  Terms  and 
Abbreviations ;  of  the  Instruments,  Drugs,  Diseases,  Accidents,  Treat- 
ments, Operations,  Foods,  Appliances,  etc.  encountered  in  the  ward  or 
in  the  sick-room.  By  HONNOR  MORTEN,  author  of  "  How  to  Become 
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Raymond's  Physiology.    Rev-uJ^Tot^°^^ 

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Professor  of  Physiology  and  Hygiene  and  Lecturer  on  Gynecology  in 
the  Long  Island  College  Hospital. 

Salinger  and  Kalteyer's  Modern  Medicine. 

Modern  Medicine.  By  JULIUS  L.  SALINGER,  M.  D.,  Demonstrator  of 
Clinical  Medicine,  Jefferson  Medical  College;  and  F.  J.  KALTEYER, 
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Saundby's  Renal  and  Urinary  Diseases. 

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Saunders'  Medical  Hand-Atlases. 

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OF   W.  B.  SAUNDERS   &    CO.  13 

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1.  Essentials  of  Physiology.     By  SIDNEY  BUDGETT,  M.  D.     A  New  Work. 

2.  Essentials  of  Surgery.     By  EDWARD  MARTIN,  M.D.     Seventh  edition,  revised,  with 

an  Appendix  and  a  chapter  on  Appendicitis. 

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oughly revised  and  enlarged. 

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M.  D.     Fifth  edition,  revised. 

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and  enlarged. 

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on  URINE  EXAMINATION.  By  LAWRENCE  WOLFF,  M.  D.  Third  edition,  enlarged 
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edition,  revised  and  enlarged. 

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present  out  of  print. 

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15.  Essentials  of  Diseases  of  Children.    By  WILLIAM  M.  POWELL,  M.  D.    Third  edition. 

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18.  Essentials    of   Practice   of   Pharmacy.     By  Lucius   E.   SAYRE.     Second   edition, 

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19.  Essentials  of  Diseases  of  the  Nose  and  Throat.     By  E.  B.  GLEASON,  M.  D.     Third 

edition,  revised  and  enlarged. 

20.  Essentials  of  Bacteriology.     By  M.  V.  BALL,  M.  D.     Fourth  edition,  revised. 

21.  Essentials  of  Nervous  Diseases  and  Insanity.     By  JOHN  C.  SHAW,  M.  D.     Third 

edition,  revised. 

22.  Essentials  of   Medical   Physics.     By  FRED  J.  BROCKWAY,  M.D.     Second  edition, 

revised. 

23.  Essentials  of  Medical  Electricity.     By  DAVID  D.  STEWART,  M.  D.,  and  EDWARD 

S.  LAWRANCE,  M.  D. 

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revised  and  greatly  enlarged. 

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Atlas  and   Epitome  of   Syphilis    and  the  Venereal 
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Atlas  and  Epitome  of  External  Diseases  of  the  Eye. 

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By  DR.  ED.  GOLEBIEWSKI,  of  Berlin.  Translated  and  edited  with  addi- 
tions by  PEARCE  BAILEY,  M.  D.,  Attending  Physician  to  the  Department 
of  Corrections  and  to  the  Almshouse  and  Incurable  Hospitals,  New 
York.  With  40  colored  plates,  143  text-illustrations,  and  600  pages 
of  text.  Cloth,  $4.00  net. 

Atlas  and  Epitome  of  Gynecology. 

By  DR.  O.  SHAEFFER,  of  Heidelberg.  From  the  Second  Revised  Ger- 
man Edition.  Edited  by  RICHARD  C.  NORRIS,  A.M.,  M.  D.,  Gyne- 
cologist to  the  Methodist  Episcopal  and  the  Philadelphia  Hospitals; 
Surgeon -in -Charge  of  Preston  Retreat,  Philadelphia.  With  90  colored 
plates,  65  text-illustrations,  and  308  pages  of  text.  Cloth,  $3.50  net. 

Atlas  and  Epitome  of  the  Nervous  System  and  its 
Diseases. 

By  PROFESSOR  DR.  CHR.  JAKOB,  of  Erlangen.  From  the  Second  Re- 
vised and  Enlarged  German  Edition.  Edited  by  EDWARD  D.  FISHER, 
M.  D.,  Professor  of  Diseases  of  the  Nervous  System,  University  and 
Bellevue  Hospital  Medical  College,  New  York.  With  83  plates  and  a 
copious  text.  Cloth,  $3.50  net. 

Atlas  and  Epitome  of  Labor  and  Operative  Obstetrics. 

By  DR.  O.  SCHAEFFER,  of  Heidelberg.  From  the  Fifth  Revised  and 
Enlarged  German  Edition.  Edited  by  J.  CLIFTON  EDGAR,  M.  D., 
Professor  of  Obstetrics  and  Clinical  Midwifery,  Cornell  University 
Medical  School.  With  126  colored  illustrations.  Cloth,  $2.00  net. 

Atlas    and     Epitome    of    Obstetric     Diagnosis    and 
Treatment. 

By  DR.  O.  SCHAEFFER,  of  Heidelberg.  From  the  Second  Revised  and  En- 
larged German  Edition.  Edited  by  J.  CLIFTON  EDGAR,  M.  D.,  Professor 
of  Obstetrics  and  Clinical  Midwifery,  Cornell  University  Medical  School. 
72  colored  plates,  text-illustrations,  and  copious  text.  Cloth,  $3.00  net. 

Atlas   and   Epitome   of  Ophthalmoscopy  and    Oph- 
thalmoscopic    Diagnosis. 

By  DR.  O.  HAAB,  of  Ziirich.  From  the  Third  Revised  and  Enlarged 
German  Edition.  Edited  by  G.  E.  DE  SCHWEINITZ,  M.  D.,  Professor 
of  Ophthalmology,  Jefferson  Medical  College,  Philadelphia.  With  152 
colored  figures  and  82  pages  of  text.  Cloth,  $3.00  net. 

Atlas  and  Epitome  of  Bacteriology. 

Including  a  Text-Book  of  Special  Bacteriologic  Diagnosis.  By  PROF. 
DR.  K.  B.  LEHMAXN  and  DR.  R.  O.  NEUMANN,  of  Wurzburg.  From  the 
Second  Revised  German  Edition.  Edited  by  GEORGE  H.  WEAVER,  M.  D., 
Assistant  Professor  of  Pathology  and  Bacteriology,  Rush  Medical  College, 
Chicago.  Two  volumes  with  over  600  colored  lithographic  figures, 
numerous  text-illustrations,  and  500  pages  of  text. 


ADDITIONAL  VOLUMES   IN   PREPARATION. 

17 


NOTHNAGEL'S  ENCYCLOPEDIA 

OF 

PRACTICAL   MEDICINE 

Edited  by  ALFRED   STENGEL,  M.  D. 

Professor  of  Clinical  Medicine  in  the  University  of  Pennsylvania;  Visiting 
Physician  to  the  Pennsylvania  Hospital 

ris  universally  acknowledged  that  the  Germans  lead  the  world  in  Internal 
Medicine  ;  and  of  all  the  German  works  on  this  subject,  Nothnagel's  "  Ency- 
clopedia of  Special  Pathology  and  Therapeutics"  is  conceded  by  scholars  to 
be  without  question   the   best  System   of  Medicine  in  existence.      So  necessary 
is  this  book  in  the  study  of  Internal  Medicine  that  it  comes  largely  to  this  country 
in  the  original  German.     In  view  of  these  facts,  Messrs.  W.  B.  Saunders  &  Com- 
pany have  arranged  with  the  publishers  to  issue  at  once  an   authorized   edition 
of  this  great  encyclopedia  of  medicine  in  English. 

For  the  present  a  set  of  some  ten  or  twelve  volumes,  representing  the  most 
practical  part  of  this  encyclopedia,  and  selected  with  especial  thought  of  the  needs 
of  the  practical  physician,  will  be  published.  The  volumes  will  contain  the  real 
essence  of  the  entire  work,  and  the  purchaser  will  therefore  obtain  at  less  than 
half  the  cost  the  cream  of  the  original.  Later  the  special  and  more  strictly 
scientific  volumes  will  be  offered  from  time  to  time. 

The  work  will  be  translated  by  men  possessing  thorough  knowledge  of  both 
English  and  German,  and  each  volume  will  be  edited  by  a  prominent  specialist 
on  the  subject  to  which  it  is  devoted.  It  will  thus  be  brought  thoroughly  up  to 
date,  and  the  American  edition  will  be  more  than  a  mere  translation  of  the  Ger- 
man ;  for,  in  addition  to  the  matter  contained  in  the  original,  it  will  represent  the 
very  latest  views  of  the  leading  American  specialists  in  the  various  departments 
of  Internal  Medicine.  The  whole  System  will  be  under  the  editorial  super- 
vision of  Dr.  Alfred  Stengel,  who  will  select  the  subjects  for  the  American  edition, 
and  will  choose  the  editors  of  the  different  volumes. 

Unlike  most  encyclopedias,  the  publication  of  this  work  will  not  be  extended 
over  a  number  of  years,  but  five  or  six  volumes  will  be  issued  during  the  coming 
year,  and  the  remainder  of  the  series  at  the  same  rate.  Moreover,  each  volume 
will  be  revised  to  the  date  of  its  publicatfon  by  the  American  editor.  This  will 
obviate  the  objection  that  has  heretofore  existed  to  systems  published  in  a  number 
of  volumes,  since  the  subscriber  will  receive  the  completed  work  while  the  earlier 
volumes  are  still  fresh. 

The  usual  method  of  publishers,  when  issuing  a  work  of  this  kind,  has  been 
to  compel  physicians  to  take  the  entire  System.  This  seems  to  us  in  many  cases 
to  be  undesirable.  Therefore,  in  purchasing  this  encyclopedia,  physicians  will  be 
given  the  opportunity  of  subscribing  for  the  entire  System  at  one  time  ;  but  any- 
single  volume  or  any  number  of  volumes  may  be  obtained  by  those  who  do  not 
desire  the  complete  series.  This  latter  method,  while  not  so  profitable  to  the  pub- 
lisher, offers  to  the  purchaser  many  advantages  which  will  be  appreciated  by  those 
who  do  not  care  to  subscribe  for  the  entire  work  at  one  time. 

This  American  edition  of  Nothnagel's  Encyclopedia  will,  without  question, 
form  the  greatest  System  of  Medicine  ever  produced,  and  the  publishers  feel  con- 
fident that  it  will  meet  with  general  favor  in  the  medical  profession. 


NOTHNAGEL'S  ENCYCLOPEDIA 

VOLUMES  JUST  ISSUED  AND  IN  PRESS 


VOLUME  I 
Editor,  William  Osier,  M.D.,  F.R.C.P. 

Professor  of  Mcdici:ie  in  Johns  Hopkins 

University 

CONTENTS 

Typhoid  Fever.  By  DR.  H.  CURSCHMANN, 
of  Leipsic.  Typhus  Fever.  By  DR.  H. 
CURSCHMANN,  of  Leipsic. 

Handsome  octavo  volume  of  about  600  pages. 
Just  Issued 


VOLUME  II 

Editor,  Sir  J.  W.  Moore,  B.  A.,  M.D., 
F.R.C.P.I.,  of  Dublin 

Professor  of  Practice  of  Medicine,  Royal  College 
of  Surgeons  in  Ireland 

CONTENTS 

Erysipelas  and  Erysipeloid.  By  DR.  H.  LEN- 
HARTZ,  of  Hamburg.  Cholera Asiatica  and 
Cholera  Nostras*  By  DR.  K.'VON  LIEBER- 
MEISTER,  of  Tiibingen.  "Whoooing  Cough 
and  Hay  Fever.  By  DR.  G.  STICKER,  of 
Giessen.  Varicella.  By  DR.  TH.  VON  JUR- 
GENSEN, of  Tubingen.  Variola  (including 
Vaccination).  By  DR.  H.  IMMERMANN,  of 
Basle. 

Handsome  octavo  volume  of  over  700  pages. 
Just  Issued 


VOLUME  VII 
Editor,  John  H.  Musser,  M.  D. 

Professor  of  Clinical  Medicine,  University  of 
Pennsylvania 

CONTENTS 

Diseases  of  the  Bronchi.  By  DR.  F.  A.  HOFF- 
MANN, of  Leipsic.  Diseases  of  the  Pleura. 
By  DR.  ROSENBACH,  of  Berlin.  Pneumonia, 
By  DR.  E.  AUFRECHT,  of  Magdeburg. 


VOLUME  VIII 
Editor,  Charles  G.  Stockton,  M.  D. 

Professor  of  Medicine,  University  of  Buffalo 
CONTENTS 

Diseases  of  the  Stomach.    By  DR.  F.  RIEGEL, 

of  Giessen. 


VOLUME  IX 
Editor,  Frederick  A.  Packard,  M.  D. 

Physician  to  the  Pennsylvania  Hospital  and  to  the 
Children' s  Hospital,  Philadelphia 

CONTENTS 

Diseases  of  the  Liver.    By.  DRS.  H.  QUINCKE 
and  G.  HOPPE-SEYLER,  of  Kiel. 


VOLUME  m 

Editor,  William  P.  Northrup,  M.  D. 

Professor  of  Pediatrics,  University  and  Bellevue 
Medical  College 

CONTENTS 

Measles.  By  DR.  Tn.  VON  JURGENSEN,  of 
Tubingen.  Scarlet  Fever.  By  the  same 
author.  Rotheln.  By  the  same  author. 


VOLUME  X 
Editor,  Reginald  H.  Fit*,  A.M.,  M.  D. 

Hersey  Professor  of  the  Theory  and  Practice 
of  Physic,  Harvard  University 

CONTENTS 

Diseases  of  the  Pancreas.  By  DR.  L.  OSER, 
of  Vienna.  Diseases  of  the  Suprarenals. 
By  DR.  E.  NEUSSER,  of  Vienna. 


VOLUME  VI 
Editor,  Alfred  Stengel,  M.  D. 

Professor  of  Clinical  Mt'dicinc,  University  of 
Pen  nsylra  n  ta 

CONTENTS 

Anemia.  By  DR.  P.  EHRLTCH,  of  Frankfort  - 
on-the-Main,  and  DR.  A.  LAZARUS,  of  Char- 
lottenburg.  Chlorosis.  By  DR.  K.  vox 
NOORDEN,  of  Frankfort-on-the-Main.  Dis- 
eases of  the  Spleen  and  Hemorrhagic 
Diathesis.  By  DR.  M.  LITTI.N,  of  Berlin. 


VOLUMES  IV,  V,  and  XI 
Editors  announced  later 

Vol.  IV.— Influenza  and  Dengue.  By  DR.  O. 
LEICHTENSTERN,  of  Cologne.  Malarial  Dis- 
eases. By  DR.  J.  MANNABERG,  of  Vienna. 

Vol.  V. — Tuberculosis  and  Acute  General 
Miliary  Tuberculosis.  By  DR.  G.  CORNET, 
of  Berlin. 

Vol.  XL— Diseases  of  the  Intestines  and 
Peritoneum.  By  DR.  H.  NOTHNAGEL, 
of  Vienna. 


CLASSIFIED  LIST 

or  THE 

MEDICAL   PUBLICATIONS 


or 


W.  B.  SAUNDERS  &  COMPANY 


ANATOMY,  EMBRYOLOGY, 
HISTOLOGY. 

Bblim,  Davidoff,  and  Huber— A  Text- 
Book  of  Histology, 

Clarkson— A  Text-Book  of  Histology,  .    . 

Haynes — A  Manual  of  Anatomy 

Heisler— A  Text-Book  of  Embryology,  .    . 

Leroy— Essentials  of  Histology 

Nancrede — Essentials  of  Anatomy,  .... 

Nancrede — Essentials  of  Anatomy  and 
Manual  of  Practical  Dissection,  .... 

BACTERIOLOGY. 

Ball — Essentials  of  Bacteriology 

Frothingham — Laboratory  Guide,  .... 

Gorham — Laboratory  Course  in  Bacteri- 
ology  

Lehmann  and  Neumann — Atlas  of  Bacte- 
riology  

Levy  and  Klemperer's  Clinical  Bacteri- 
ology  

Mallory  and  Wright — Pathological  Tech- 
nique,   

McFarland — Pathogenic  Bacteria 

CHARTS,  DIET-LISTS,  ETC. 

Griffith — Infant's  Weight  Chart 

Hart— Diet  in  Sickness  and  in  Health,  .    . 

Keen— Operation  Blank 

Laine — Temperature  Chart 

Meigs — Feeding  in  Early  Infancy 

Starr — Diets  for  Infants  and  Children,  .    . 
Thomas— Diet-Lists 


CHEMISTRY  AND  PHYSICS. 

Brockway— Essentials  of  Medical  Physics, 
Wolff—  Essentials  of  Medical  Chemistry,  . 

CHILDREN. 
An  American  Text-Book  of  Diseases  of 

Children 

Griffith— Care  of  the  Baby 

Griffith— Infant's  Weight  Chart 

Meigs — Feeding  in  Early  Infancy,  .... 
Powell— Essentials  of  Diseases  of  Children, 
Starr— Diets  for  Infants  and  Children,  . 

DIAGNOSIS. 

Cohen  and  Eshner — Essentials  of  Diag- 
nosis,  

Corwin — Physical  Diagnosis, 

Vierordt— Medical  Diagnosis 

DICTIONARIES. 

The  American  Illustrated  Medical  Dic- 
tionary,    

The  American  Pocket  Medical  Dictionary, 
Morten — Nurses'  Dictionary, 


EYE,  EAR,  NOSE,  AND  THROAT. 

An  American  Text-Book  of  Diseases  of 

the  Eye,  Ear,  Nose,  and  Throat i 

De  Schweinitz — Diseases  of  the  Eye,    .    .     6 
Friedrich  and  Curtis— Rhinology,  Laryn- 
gology and  Otology .     6 

Gleason — Essentials  of  Diseases  of  the  Ear,    15 
Gleason — Ess.  of  Dis.  of  Nose  and  Throat,    15 

Gradle — Ear,  Nose,  and  Throat, 22 

Griinwald  and    Grayson— Atlas  of  Dis- 
eases of  the  Larynx 16 

Haab  and  De  Schweinitz — Atlas  of  Exter- 
nal Diseases  of  the  Eye 

Haab  and  De  Schweinitz— Atlas  of  Oph- 

thalmoscopy, 

Jackson — Manual  of  Diseases  of  the  Eye, 
Jackson — Essentials  of  Diseases  of  Eye, 
Kyle— Diseases  of  the  Nose  and  Throat,  . 


16 


GENITO-URINARY. 


An  American  Text-Book  of  Genito-Uri- 

nary  and  Skin  Diseases 2 

Hyde  and  Montgomery— Syphilis  and  the 

Venereal  Diseases, 8 

Martin — Essentials  of  Minor  Surgery, 

Bandaging,  and  Venereal  Diseases,  ...  15 
Mracek  and  Bangs — Atlas  of  Syphilis  and 

the  Venereal  Diseases 16 

Saundby — Renal  and  Urinary  Diseases,  .  .  n 

Senn — Genito-Urinary  Tuberculosis,  ...  12 

Vecki— Sexual  Impotence 14 

GYNECOLOGY. 

American  Text-Book  of  Gynecology,   .    .  2 

Cragin — Essentials  of  Gynecology 15 

Garrigues — Diseases  of  Women 6 

Long — Syllabus  of  Gynecology, 9 

Penrose — Diseases  of  Women 10 

Pryor — Pelvic  Inflammations n 

Schaefler  &  Norris — Atlas  of  Gynecology,  17 

HYGIENE. 

Abbott — Hygiene  of  Transmissible  Diseases    3 

Bergey — Principles  of  Hygiene 22 

Pyle — Personal  Hygiene n 

MATERIA  MEDICA,  PHARMACOL- 
OGY, AND  THERAPEUTICS. 

American  Text-Book  of  Therapeutics,  .    .  i 
Butler — Text-Book    of    Materia    Medica, 

Therapeutics,  and  Pharmacology,   ...  4 

Morris— Ess.  of  M.  M.  and  Therapeutics,  15 

Saunders'  Pocket  Medical  Formulary,  .    .  n 

Sayre— Essentials  of  Pharmacy 15 

Sollmann — Text- Book  of  Pharmacology,  .  22 

Stevens— Manual  of  Therapeutics,    ...  13 

Stoney — Materia  Medica  for  Nurses,   .    .  13 

Thornton — Prescription- Writing,    ....  13 


20 


MEDICAL  PUBLICATIONS  OF  W.  B.  SAUNDERS  &>  CO.    21 


MEDICAL  JURISPRUDENCE  AND 
TOXICOLOGY. 

Chapman — M  e  d  i  c  a  1  Jurisprudence  and 
Toxicology 5 

Golebiewski  and  Bailey— Atlas  of  Dis- 
eases Caused  by  Accidents 17 

Hofmann  and  Peterson— Atlas  of  Legal 
Medicine 16 

NERVOUS  AND  MENTAL 
DISEASES,  ETC. 

Brower — Manual  of  Insanity 22 

Chapin — Compendium  of  Insanity,    ...      5 
Church  and  Peterson — Nervous  and  Men- 
tal Diseases 5 

Jakob  &  Fisher — Atlas  of  Nervous  System,    17 
Shaw — Essentials  of  Nervous  Diseases  and 
Insanity, 15 

NURSING. 

Davis — Obstetric  and  Gynecologic  Nursing,  6 

Griffith— The  Care  of  the  Baby 7 

Hart — Diet  in  Sickness  and  in  Health,   .    .  7 

Meigs — Feeding  in  Early  Infancy,  .    .    .    .  10 

Morten — Nurses'  Dictionary 10 

Stoney— Materia  Medica  for  Nurses,     .    .  13 

Stoney — Practical  Points  in  Nursing,  ...  13 

Stoney — Surgical  Technic  for  Nurses,    .    .  13 

Watson— Handbook  for  Nurses,     ....  14 

OBSTETRICS. 

An  American  Text-Book  of  Obstetrics,    .  2 

Ashton — Essentials  of  Obstetrics 15 

Boisliniere — Obstetric  Accidents 4 

Borland — Modern  Obstetrics 6 

Hirst — Text-Book  of  Obstetrics 7 

Norris — Syllabus  of  Obstetrics, 10 

Schaeffer  and  Edgar — Atlas  of  Obstetri- 
cal Diagnosis  and  Treatment 17 

PATHOLOGY. 

An  American  Text-Book  of  Pathology,  .  2 
Durck  and  Hektoen— Atlas  of  Pathologic 

Histology 16 

Kalteyer — Essentials  of  Pathology,    ...    15 
Mallory  and  Wright— Pathological  Tech- 
nique         .....     9 

Senn — Pathology  and  Surgical  Treatment 

of  Tumors 12 

Stengel— Text-Book  of  Pathology,    ...    12 
Warren— Surgical  Pathology  and  Thera- 
peutics  14 

PHYSIOLOGY. 

An  American  Text-Book  of  Physiology,  2 
Budgett — Essentials  of  Physiology,  ...  15 
Raymond — Text-Book  of  Physiology,  .  .  n 
Stewart—  Manual  of  Physiology,  ....  13 

PRACTICE  OF  MEDICINE. 
An  American  Year-Book  of  Medicine  and 

Surgery 3 

Anders — Practice  of   Medicine, 4 

Eichhorst — Practice  of  Medicine 6 

LockWOOd— Manual    of    the    Practice    of 

Medicine, 9 

Morris — Ess.  of  Practice  of  Medicine,  .    .    15 
Salinger  and  Kalteyer— Modern   Medi- 
cine,  ii 

Stevens — Manual  of  Practice  of  Medicine,    13 


SKIN  AND  VENEREAL. 

An    American    Text-Book    of    Genito- 
Urinary  and  Skin  Diseases 2 

Hyde  and  Montgomery — Syphilis  and  the 

Venereal  Diseases, 8 

Martin — Essentials    of     Minor    Surgery, 

Bandaging,  and  Venereal  Diseases,     .    .  15 

Mracek  and  Stelwagon— Atlas  of  Diseases 

of  the  Skin 16 

:  Stelwagon— Essentials  of  Diseases  of  the 

Skin 15 

SURGERY. 

!  An  American  Text-Book  of  Surgery,   .    .  2 
j  An  American  Year-Book  of  Medicine  and 

Surgery, 3 

Beck— Fractures 4 

Beck — Manual  of  Surgical  Asepsis,    ...  4 

Da  Costa — Manual  of  Surgery, 5 

International  Text-Book  of  Surgery,  .    .  8 

Keen — Operation  Blank 8 

Keen — The   Surgical    Complications   and 

Sequels  of  Typhoid  Fever, 8 

Macdonald — Surgical  Diagnosis  and  Treat- 
ment,    9 

Martin—  Essentials    of    Minor    Surgery, 

Bandaging,  and  Venereal  Diseases,     .    .  15 

Martin— Essentials  of  Surgery 15 

Moore — Orthopedic  Surgery 10 

Nancrede — Principles  of  Surgery 10 

Pye — Bandaging  and  Surgical  Dressing,    .  n 

Scudder — Treatment  of  Fractures,     ...  12 

Senn— Genito-Urinary  Tuberculosis,  ...  12 

Senn — Practical  Surgery 12 

Senn — Syllabus  of  Surgery, 12 

Senn — Pathology  and  Surgical  Treatment 

of  Tumors 12 

Warren — Surgical  Pathology  and  Thera- 
peutics   14 

Zuckerkandl  and   Da   Costa— Atlas    of 

Operative  Surgery 16 

URINE  AND  URINARY  DISEASES. 

!  Ogden — Clinical  Examination  of  the  Urine,  10 

Saundby — Renal  and  Urinary  Diseases,    .  n 


Wolff  —  Handbook 
tion, 

Wolff —  Essentials     of 
Urine 


of     Urine-Examina- 


Examination     of 


MISCELLANEOUS. 

Bastin — Laboratory  Exercises  in  Botany,  .     4 
Golebiewski  and  Bailey— Atlas  of  Dis- 
eases Caused  by  Accidents 17 

Gould  and  Pyle— Anomalies  and  Curiosi- 
ties of  Medicine, 7 

Grafstrom — Massage 7 

Keating— How  to  Examine  for  Life  Insur- 


Saunders'  Medical  Hand-Atlases,  .  .  16,17 
Saunders'  Pocket  Medical  Formulary,  .  .  n 
Saunders'  Question-Compends,  .  .  .  14,15 
Stewart  and  Lawrence— Essentials  of 

Medical  Electricity 15 

Thornton —  Dose-Book  and  Manual  of 

Prescription-Writing,  13 

Van  Valzah  and  Nisbet— Diseases  of  the 

Stomach 13 


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